Pittsburgh was the most frustrating area in the game, imo. Everything that comes after is much better. It was unfortunate how it wore me out though, by the point I started the more interesting Fall and Winter the impact of combat and infected was almost lost. That's probably one of my gripes about the game; it started out really well, delivering the type of intensity and nerve-racking encounters of RE4, but then the infected became common place and the game was reluctant in throwing more enemy types and scares.
In a way, it's understandable, since they didn't want to go overboard with the concept... the game tried to avoid some of the gaming cliches as much as possible, such as the monster > big monster > BIGGER MONSTER > IMPOSSIBLE BOSS! at predictable, designated points. It was a refreshing change, albeit one at the expense of the aforementioned intense scares.