Indeed a big shame Silvestri didn't incorporate more themes. Of course it's obvious that Iron Man, Black Widow and Hawkeye have no themes to speak of with the bad soundtracks to Iron Man 1 and 2, but come on: Doyle's take on Thor was sublime and Armstrong's themes (for both Bruce Banner as the Hulk) really hit a nerve with this listener.
The only theme I can really hear is Captain America and unfortunately (correct me if I'm wrong) it's just a few seconds during the track 'Subjugation' where Silvestri drops some notes, but other then that, none whatsoever.
I don't dislike the soundtrack for this, it's a really great soundtrack amongst all the RC/MV stuff that's coming out (Battleship being another example of that), it's just that it could've been a little bit better had he incorporated some themes that were just lying there for the taking.
Still...I can't deny the Avengers theme is one wonderful theme that will get your blood pumping, alongside tracks as 'A Promise', 'Arrival' and of course the sweet and emotional 'They Called It', which really was nice and conveyed the groups feelings towards the death of you know who.