My impressions so far?
Other than some spawn issue's I've had I'm actually enjoying this beta a lot.
Reminds me of playing Halo CE at a afterschool social club I went to when it came out.
The health system I quite like, I'm not seeing any of these grenade spam issues people are complaining about.
Halo was always about Guns, grenades, Melee and that is how it should remain, You start off with 2 grenades and if you are lucky you will get 2 kills with them which isn't really something to be raging about.
More often than not I get kills by assassinations or the magnum.

I noticed they've decreased the shots fired by the Spartan laser down to 4 shot's which took me by surprise a little, for a day or so I avoided the pistol but at one point I was forced to use it and realised just how decent it was in close range.
My current opinion is this is what Halo 2 should have been like, same with Halo 3.
I can see myself playing invasion an awful lot if they fix the spawn issues, I was spawning in the middle of no cover as a elite and being picked off until I used the load out with the evade ability.