The Citadel portions were small in ME2 because rather than getting a large urban hub, as there was in ME1, there were 3 hubs: The Citadel, Illium, and Omega.
While in ME3 the Citadel was the only hub, I think it is much more alive than the ME1's version particularly if you include the Citadel DLC and the Silversun Strip. ME1's version of the Citadel is a a bit overrated out of nostalgia, IMO. It was vast but largely empty.
+1, I dunno where the idea that Bioware can't do cities came from, but it's a bit unfair. The Citadel DLC's strip was amazing.
I think the weird part was that Val Royeux was described as being this vast metropolis at the centre of an Empire. To find it's actually just a big building with a population of less than 50 was a tad underwhelming, particularly since Bioware have repeatedly demonstrated that they have a knack for making cities to appear much larger than they actually are. I mean, just remember Taris.