There are loads of cues from ACB that I love, unfortunately I haven't gotten the full album yet, it definitely has a more cinematic and ominous tone as AC2. The Venice Rooftop theme is a standout for sure, didn't take to it at first, but it grew on me. The theme was used once so far in ACB as far as I can recall.
Yeah Hans Zimmer was the guy who got me into the genre, the first CD I bought that wasn't metal, was The Rock soundtrack! I've since bought pretty much everything he's released (Da Vinci Code and Angels and Demons - do yourself a favor!)
My favorite composer is James Newton Howard, you should check out some of his stuff.