I can do little but echo PhilBowles great as always write-up, so I'll just summarize: did you actually like the things that CiV did differently? Did you like SPs and 1UPT, the whip and draft being replaced by gold rush, both tall and wide empires being equally viable choices? If not, well, the game
is the same, just better balanced. They didn't add things from IV, V was never intended to be Civ 4.5. If you thought though that it had a lot of potential, but was unbalanced and unfinished, then yes, it's been fixed.
My 2 cents as someone who hated the game at launch, but really wanted to like it:
Buildings are very much worth building. Maintenances have been adjusted multiple times, almost always getting lowered, and I think on that account they have done quite well. The growth formula for cities has been changed, so now cities actually grow beyond size 10. Production has been sped up noticeably. SPs have been tweaked so much (Piety in particular) that I feel some of the trees barely resemble their counterparts at launch. Your choice between the last 3 Sp trees also has an influence on diplomacy just like civics in IV. Happiness has seen numerous changes. In the last vanilla version it was quite the challenge to balance it out, in G+K it's easier and leaves you some more room to expand. Now each city can't generate more happiness than its pop size, introducing local happiness that's part of the global. Just goes to show you that the whole system isn't really that good, but it works well enough, I don't mind it.
The expansion did a lot of good things too. Diplomacy has been improved and it is now possible to be at good terms with other civs. It's also more transparent (even if more could be done here) and it's generally easier to evaluate how much a civ AI likes or hates you. The tactical AI has also been improved - while it's better, calling it "good" would steel be a bit of an overstatement, but it's light-years away from what we had at launch. Currently there is this weird thing where some civs just don't expand at all, but I am sure they will iron it out with a patch. G+K also brought probably the biggest redesign of the tech tree I have seen in a Civ game, all for the better, now it actually deserves to be called a tech tree (as opposed to a ladder) and researching is considerably slower, which means that now you don't obsolete units before you even get a chance to build them. All GPs except the merchant have been tweaked, GS bulbing doesn't work the way it did before, neither do RAs (another feature that has nothing to do with its initial version when the game launched). City States offer way more quests than before and they are generally a lot more fun to do as well, while gold has been nerfed quite a lot. In the late game buying them out is very much the best tactic, but until around late-Renaissance or early Industrial you won't be able to do that.
There are still some oddities, particularly with the AI and the warmonger diplo penalty is still curiously annoying at times, but the game is
much better now. I don't know what constitutes in your opinion a builder game as opposed to a war game though, so can't comment on that, although I could argue that Civ has always had a warming heart for better or worse. For me the big problem before was low production (fixed IMO), too fast teching (fixed), really slow growth (fixed) and nothing to do beyond choosing what to build and research. That last bit was remedied by the truly great religion and Espionage, which, while underwhelming, still brings flavour. Also lets you steal tech, which is nice.
There is a G+K demo on Steam, I suggest you try it out. You might hate it for all I know, but as someone who is a builder and was gravely disappointed by V at launch, the recent patches and the expansion made me change my views. Same goes for PhilBowles for example. It might be more streamlined than IV, but I actually like that, in the late game CIV sometimes just got tedious with all the micromanagement.
But then again, I thought that CIV BTS was a bit bloated (corps, espionage, health? Would be better off without them), so maybe I'm out of line here.