Hi, I have just signed for posting this, but I have been lurking on and off here at CFC since coming across this site in 2003, after having played Civ 3 for a while. I enjoyed that game a lot, and even more in the case of Civ 4. Although I never bought Civ 5, mostly because my always-busy schedule kept draining away my gaming-time

, and in a minor part because I still played Civ 4 in the rare opportunities I did have, I was really looking forward for this game. When I did return to the forums, about one month after this games release, I was underwhelmed by the fact that half the threads about it where about wheter this game sucked or not. Then I decided to try the demo (since MOO3

, I always try demos first before buying) and while it did was different, I didnt have fun (Yeah, I know that 100 turns is not enough to judge the game, but this, for me at least, is the most fun period in Civ games, since it is when most of the game changing decisions are taken), in contrast to the Civ 4 demo which hooked me into the game almost instantly. So my answer to the OPs question would be that Civ 5 is not worth the cash, not for now at least.
Now slightly off-topic:
I have seen a lot of times stuff like this mentioned in topics comparing Civ 4 to Civ 5, and while I do realize that the reception of both Civ 3 and Civ 4 where accompanied by game dumbed down posts (which were mostly nonsense in the case of Civ 4, IMHO; OTOH, I wasn't here by the time of 3) about the new game and complaints about technical issues(by what I heard, particularly in Civ 3s release, but there were quite a few in 4 too), I do feel that the numerous claims that Civ 4 only became good when the BTS expansion was released are really overblown. There is a difference between being good and being considered good, which of course depends on individual tastes, but I never found great differences introduced on the game as a whole by either Warlords or BTS, both of which I always found as rather lacking expansion packs (most of their changes that I would end up liking were more similar to patches than an expansion). Lets take a look:
Warlords:
Positive:
Fixes to combat: chariot bonus vs. Axes and cost increase to 30(in vanilla, Axes could be countered effectively only by WEs or HAs, or having Aggressive Axemen; OTOH, WCs and Immortals were ridiculously cheap for their power, especially since the AI neglected to build Spearmen for a long time), eventually preventing siege units to kill (via a patch, IIRC) and introduction of Great Generals.
Inclusion of the Blakes AI in the core game.
Introduction of UBs, which added some interesting choices to the game (although most of them had few impact overall, while a few were overpowered - especially the incan Terrace).
Negative:
Vassal states: IMHO, the most stupid feature in Civ 4. Yes, they have the "nice goal" of allowing speeding up a domination victory, eliminating tedium in the mop up phase. However, its implementation means that if I DOW one of my 2 neighbors and during our war he capitulates to my other neighbor, that second neighbor immediately DOWs me, in a completely random fashion and with little regard to past relations, and of course if this is a high difficulty level, youre propably screwed!

Almost always Im forced to use Custom Game because of this.
A series of reworkings to the traits system: addition of the sucky protective trait, which does nothing but make conquering AIs a pain with their CG3 Longbows and doing nothing to help their expansion or economy (and before it is said that Aggressive belongs to the same boat, remember that it at least helps the AI with invasion or counter-attack in their own territory, whereas Protective serves to
Stack defenders in city to be destroyed by collateral damage?

Not to mention that Aggressive helps a tiny bit in the early game since the AI loves to stupidly build Barracks first in their cities and delay their development, or build Barracks in the capital 30 turns into the game, when they have at most 3 cities on normal speed, Deity difficulty. Protectives only real utiliy is maybe in a raging barbs environment, or perhaps AW for the human), the overpowered Expansive trait (50% worker production bonus in Warlords!) and some overpowered Civ/Leader combinations(FIN/IND Huayna with
de facto CRE trait from UB, as if the UU wasnt enough, CRE/ORG Augustus with CRE turning the Praetorian rush even more into a steamroll with the easier acess to Iron from the expanded borders and the faster border-popping in conquered cities, and FIN/ORG Darius with a very powerful Rush UU and perfect trait to support new conquests).
BTS:
Positive:
More improvements to the AI thanks to Blakes project incorporated into the game, allowing some reduction of the higher levels handicaps.
Some fixes to combat, such as the introduction of Cuirassiers which delayed a bit the arrival of Cavalry(it was way too powerful beelining Military Tradition and Gunpowder before the enemy reached Rifling, although still weaker than mass drafting) and delaying Grenadiers a bit, giving Muskets a bit more time in the game.
Lots of new interesting options, such as No Tech Brokering and Unrestricted Leaders, and map scripts.
New, interesting national wonders and buildings like the Levee (although lots of the new buildings, like the Industrial Park and the Customs House, were little more than gimmick).
Negative:
This expansion absolutely broke water-based maps with the intercontinental trade route bonus, which brokens the Great Lighthouse in any Island-based map(oh, 3+3+3 from trade routes + 1 from city tile = 10 minimum commerce per turn from each new city. The Great Lighthouse was very powerful before in the right conditions, but this is way over the top) and the coastal blockades, which allows the player to shut down an entire AIs economy in any Archipelago-type map if he plans carefully.
Vassal states were not enough, so they created the option for the player to create colonies. So I take the effort to go out scouting, build settlers, workers and troops to defend the faraway cities, plus the maintenance costs, all this for giving up the gains and create a new AI on the map? This is the most gimmicky thing in this game.
Some of the new world wonders are either overpowered (such as Cristo Redentor, which was even worse before patches and the AP, which enables a broken victory condition) or turn worse an already unfun game mechanic (Statue of Zeus).
Corporations completely broke the late game. State Property was too powerful in vanilla/Warlords, so this was made to compensate for the FM civic; however, they are uber in BTS (especially the Food Corp Sids Sushi in most maps)and are very tedious to use.
The fact that Walls + Castle cut bombardment damage by 75% ruins the whole medieval combat, even before taking into account the AIs Longbows. They also are uber in MP, since with just those 2 buildings any border city becomes inexpugnable (and in conjunction with the new Flanking, turns any attack with 1-move stacks impossible, since your siege will instantly be flanked away before you have time to drop the citys defenses. That, or attacking 17,7 str Longbows(100 city +25 fortification +25 city bonus +45 promos) with 12 str Knight(C1, C2). Also, naval combat was poor enough in the vanilla version with no unit counters in the sea, which was worsened with the addition of ships of the line, which are indestructible until Destroyers, unless you count the near-useless Ironclad.
A badly-implemented espionage system. I would have loved a good espionage system, but it in this current form only adds micro and opens various abuses, such as constantly changing civics of the AIs or revolting their cities to delay Spaceship parts or legendary status. The AI does not know how to use espionage effectively and wastes early commerce running espionage slider and Spy specialists, hurting its performance. It is not even useful in MP, since the new spy units reallocated to the classical age now serve as sentry units in enemy territory, leading them to being banned in most games. And if I want to turn it off, border expansions take double the time to happen, turning the game unplayable.
With all that said, I dont see why exactly people see Civ 4 expansions (well, BTS at least) as the pinnacle of the series. Mind you that I'm
not saying that they are worse - they do, in fact, add to the gameplay -, but that it wasnt the expansions that turned Civ 4 into a good game, but exactly the other way around. They added very little overall, and all the basic mechanics, both fun and unfun, are basically the same: maintenance from cities, WW, WFYABTA, tech trading(although that could be disabled), civics, happy/health system, diplomacy, rushing, trade routes, great people, inflation, etc. As such, I do not understand how a game could suddenly become the best of the series when it was struggling so much before some expansions that barely changed the gameplay at all

(as it is implied by lots of posters here at CFC).
As for the initial release version of Civ 4, while its true that there were exploits (like the infinite anarchy trick, the fact that horses could always be seen, forest chopping yielding 30 hammers from the start even outside borders and how easy it was to slingshot Civil Service) that were corrected through patching, keep in mind that these werent problems inherent with the games economy, diplomacy or whatever systems. And regarding the games AI at that stage, it is true that it was (and is) stupid at tactical levels, but it performed decently in the big picture balancing research and growth, which is more or less the base of that game. And, despite the criticism towards the Civ 4 combat AI, it was far superior to the Civ 3 one (where the AI would always direct ALL its units at one and one only place, regardless of number of enemies or endangered areas where the result was that you could tie the AI forces up by moving left and right indefinitely by feinting at their cities, not to mention military alliances with other civs against that AI which invariably would crumble for being attacked at multiple places. You also could easily bait their armies with workers - something that I did notice in the Civ 5 demo - and how they would never coordinate their attacks properly after the initial wave (they would send a never ending trickle of units, one by one, which you could easily destroy easily). And Civ 3s AI, for its turn, crushed even more those of previous civ games.
Also, please don't take the impression that I'm saying
"But Civ 5 is not Civ 4.5! Oh nos!!1!11!" or
"Civ 4 or 3 is perfect lolz!11!1Civ 5 sucksforevah!!1!" or
"Civ 5 is a new game!1! 4get about older ones!1!1!". I'm not, and if anyone respond to this along these lines, all I have to say is that you're putting words into my mouth. Just to make it clear, let me state that, in this post, I never mentioned SOD, 1UPT(BTW, it should have been named 1UPH, h = hex

), sliders vs. Civ 5 mechanisms, leader traits vs. civ traits, or any other nonsense I fail to remember right now. I'm also not criticizing Civ 5 in any aspect directly; after all, what I played of it equals to about 8 games in the demo version(limited to 100 turns, as stated above), so all I can say is that I didn't enjoy it.
Anyway, those are just my two cents (or, more likely, two dollars).