I was a huge fan of the series and absolutely adored EUII, especially with the AGC-EEP mod. But the third part? Just can't get into. Doesn't help that it runs sluggish (and I've got a decent system). That they've cut out most of the history. I've enjoyed a number of the new concepts they through in, but I don't think he vanilla game has taken advantage of the possibilities enough.
I've been waiting for a comprehensive, historical mod of the AGC variety, but I haven't checked back at the forum in a while (heh, they banned me from half of it) so I'm not sure what's there now. I've heard complaints that Civ4 is graphically too much and I agree with them to an extent. But Civ4 has a mass market audience and is looking for mass market appeal, they simply couldn't release a game that looked a few years out of date.
EU is very much a niche game for a niche market. Most of the audience would have been happy as pie to have a new game that looked like a slightly updated version of EUIII. Noone needed or wanted the 3D crap. Oh well. I still play EUII every so often, but I haven't dusted off 3 in quite a while.