I personally think Uematsu is VERY overrated. From what I've heard, he had no real formal education in music, and it shows in his work. Yes, most film composers take a lot from classical pieces, but they do it more in spirit. Uematsu very obviously borrows from Sergei Rachmaninoff, and not in spirit, but in rhythms, piano flares, etc. It's fun, and I'm not really saying it's bad. I just think he gets more credit than he deserves.
Jack Wall, on the other hand, is probably the most unique game composer these days. Listen to his stuff for Myst 3 and be blown away. Likewise, I love Giacchino (who originally did the score for the medal of honor games, arguably much better music than williams' own Saving Private Ryan). And being an RPG nut, I have to love Jeremy Soule, though his latest outing with Elder Scrolls Oblivion is actually very bland, IMO. But hey, awesome last name, right?
Halo has never impressed me as a game anyway (I feel like it's an fps for elementary schoolers - poorly-executed plot, bland and ridiculous candy alien villains, and hackneyed setting... Half Life 2 blows it away, plus, games like Deus Ex and System Shock are INFINITELY more complex) and the music is no different. Like Uematsu, they're trying to say "hey, I'm good and complex!", but in composition you have to show rather than tell. The music in Halo is just overblown crap.