First, let me say that Civ 2 was the best of the series from start to finish. It was the most addicting version of the game throughout every era, the expansions were superb, and it had the most character out of any of the games. Yes, Civ 2 with its 1995-97 graphics had more character than 3 or 4. Civ 4 was the most complex version of the game and very addictive in its own right, but it failed to be the all around best version due to the fact that it felt like such a huge chore to finish games out. The early eras of Civ 4 were the best, but the modern era's inability to be fun killed its chance to be the best all around.
I do agree that there is little to no hope for Civ 5 to be the best. Some of the changes seem irreparable right now barring the devs swallowing their pride and making sweeping changes. But they really can't do that cause then they risk alienating the minority? that seems to actually love the game. These are the radical changes that to me have ruined any potential for the game:
1. 1 UPT. Its a failure. Makes things extremely tedious, and slows the NPC turns way down to boot. They could have fixed stack of doom problems with other solutions.
2. Global happiness. An artificial leash to curtail expansion. Expansion has always been one of the fun things about previous Civs. It moves glacially in this game, and simply isn't fun.
3. Removal of the slider. How did it make the game better? What was wrong with it? The entire economic system of this game is pretty screwy right now, starting with the huge difference in value between gold and lightbulbs (a discrepancy amplified by the fact that gold buildings have no upkeep while lightbulb buildings do.) I'm sure it'll be balanced more in the future, but it all stems from the fact that they removed the slider, and they're not going to put it back in.
4. Embarcation. Call me old-fashioned, but after playing I just don't like it. There was always something to be said for the strategy of finding the time to build your transport ships. Now you can only build attack boats as escorts for your embarked troops, but even if you do so have fun trying to defend and move them all lol. Hell, call me really old fashioned but I long for the days when you could send your triremes into the ocean with the risk of getting lost at sea.
5. The graphics are soulless to me. Such high requirements and not only did they not improve things by them, but they are some of the more uninspiring graphics of the series to date, for my taste at least.
6. The great person changes from 4 are a step in the wrong direction. Instead of trying to make great people more versatile, they have made them less.
7. Bonus resources have been nerfed hard. You planned your cities around them in 4 because they meant something; here they hardly make any difference whatsoever, if any at all (hi sheep). This is extremely boring to me.
8. The entire city defense concept. Now I can send a settler somewhere, build a city, and suddenly these former settlers have the power to kill multiple battle units? Again, I see nothing wrong with the old system. Give me the ability to stack units in cities and let them defend it.
Thats just off the top of my head at the moment. I haven't played a game in a few days. Sure, some of the changes are good. Hexes, ranged combat, some more building specialization. By all means, I hope a few of those changes make it into Civ 6. But aside from that hopefully Civ 6 will be based more off 2 and 4 and forget a lot of the above from 5. Til then.... I think I may be going old school when I feel the need for some Civving. Maybe a Civ 5 miracle patch will change my opinion in the future, but until then, eh.