Civilization: Revolution is a terrific game. As a Civ player since Civ1, CivRev is actually my favorite game of the series. I can't say enough positive about it. I've been playing the Nintendo DS version, which I much prefer to the 10 min. or so Ive played on the PS3. I think it's visually beautiful and equally engrossing as the main-series Civ's.
And I recently acquired an iPhone -- I went with it instead of Android (despite my love of Google and hatred of Apple) for the single reason of getting Civ Rev on the go (er, more... the go... than I did on the DS?)
And I'm sorely disappointed. The visuals are somewhat ugly, the controls are more difficult (this one might be subjective; I only used the control pad on the DS, rather than the stylus), the map is just a tad too zoomed in. But... what else was I going to say? Actually, other than that, it's pretty much still a great game. I just place a very high premium on appearance (not graphics; I don't mind graphics on the level of Civ1, as long as they're not ugly, as in CivNet), because I find it difficult to be immersed in the game otherwise. And while CivRev iOS fails in this respect, that is a subjective failing, and it's a solid game otherwise.
Your other points:
* Difficult - Ranges from super easy to moderate-hard. I play on medium difficulty, and it's really fun.
* Battery - It's nothing terrible, as far as I've noticed.
* Buggy - Here it has the advantage of being the youngest member of the family. All the bugs were pretty much worked out by patches for the PS3 and Xbox (but not the DS -- sniff), and the iOS version came out after those. No bugs at all that I've found.
* Online/Offline - It will not make use of the internet in any way -- except for trying to access the manual, which is online. My iPhone is usually running offline.
I hope this helps. It's such a great, great game. And the DS version is so much better than the others. And that's totally my opinion.