For anyone on the fence, Reach is incredible.
Gene, the new controls have changed because they better fit with the new loadouts and absence of dual wielding (which few people bothered with in Halo 3).
As a matchmaking vet (having played some 9,500 games of Halo 2 and 3 online), I can tell you the matchmaking is refined even beyond Halo 3. The loadouts and gameplay changes are, I feel, all for the better (less auto-aim, less forgiving weapons, shortened melee distance, more destructable vehicles, etc). If you like online Halo, Reach is the zenith.
Loves me some Halo!