Not perfect, but lots of fun and an improvement to the series.
BUT all of the above does not make this a weak game, in my opinion it's the best in the series, and yes I have been playing since Civ 1, up until this point I'd consider 3 the worst in the series and 2 probably edging out 4 as the best, but that is a close one.
Civ 5 feels more like the older versions of the game where it feels like you're leading a nation through it's years as the empire slowly grows from a collection of cities into a nation. One thing that I have personally loved is the ability to have a real war in the ancient era. In Civ 4 I always felt that I needed to get at least Swordsman or Catapults before even attempting to go to war, which usually meant it was already 1 AD. In a couple games on standard difficultly I've been able to take over the "known world" by 1 AD much like many of the civilizations that are represented in the game. For example Alexander didn't have riflemen when he took over Asia minor, he did it with spearmen, and you can do that here.
The improvements are for the most part all positive. Hexs are great, no stacking makes war feel like war, city states add a little something, no need to build transports is awesome, gold to buy production, puppet cities (I really like this one for some reason).
Overall the game just feels more organic to me and flows better, it feels like every turn I'm doing something important; buying units, improving tiles, hunting down barbarians, positioning myself to fight a rival civ. And I wouldn't say the game has been dumbed down at all. I think that they made it simplier to jump into the game and just start playing, but if you want to go crazy microing your empire for higher levels it's there.
The game is fantastic (albeit with a few things a patch will fix) if you like the series you probably already have it and if you haven't bought it because you're afraid of the negative things you've heard, ignore the trolls, it's a fun game. If you're new to the series get the demo and see if the gameplay is your thing, if you like the type of game it is, buy it becuase it only gets better the deeper you go.