From my limited play last night, it took a bit to click with me. I do like it so far. Matchmaking took about two minutes to start up, after which it was faster than expected, and my connection seemed solid for each of the games. It doesn't feel just like older Halo games, but after a bit it felt more like a design decision than a shortcoming. I don't think it plays too closely to other games out there, though the new mechanics made the shift into my normal Recon control scheme a little odd at first.
(1) The shield vs health balance was something I appreciated. None of the weapons felt like pointless duds, and as much as luck or clever movement could stretch out the effectiveness of the shields, not much can save you once they drop, barring another player totally flubbing. This felt right.
(2) The boost, once I remembered to use it, was as interesting as an offensive tactic as defensive. Being able to cut *into* a guarded space keeps the "guaranteed" amount of damage you would get going through an entryway in flux. The best thing I saw was people using their own boost in response to quickly account for another player's movement and keep their shots lined up.
(3) The battle-banter was actually pretty interesting as a strategic element. I wasn't sure at first, but I realized having things like the power-weapon shout-outs or death locations wasn't that different from having players on your team conveying the same info. It made the focus on individual firefights that much more directed.
(4) Line of sight seemed to be deliberately controlled, and the clamber traversal seemed like a big part of that. Having surfaces that go above your normal jump height let the level design have more long-shot barriers without actually gating off movement areas.
(5) As a corollary to number 4, the vertical game was exciting without resorting to exaggerated environment heights (meaning risk-reward is still at play, because the verticality isn't enough to obscure you from most ground-level players).
(6) The music was not my style at all. I'd be happy with a full re-write.