I really enjoyed a lot of the changes, but there are of coarse a bunch of small tweaks that I think need to be made. Here are some of my inital impressions, but I will need to play more to really get a grasp on in.
-Kill Cams: we need to have the option to turn it off! I personally don't like it, but I'm sure some people will, so just give us the option to turn it off for the full game next year.
-Sensitivity: Now this is just me personally, but I felt like they turned up the base sensitivity, and had to turn it down to 2. I'm not saying they need to change this, just noting that this is the first time I have had to adjust the base sensitivity for a Halo game.
Tutorial: Halo 5 has a much bigger learning curve then any Halo before it because they have added so many new abilities to it, so a short and sweet tutorial (for the MP in full game) would be nice.
Controls: I felt that the controls were good overall, but that the ground pound in particular felt too unnatural to pull off. I would rather press a actual button in the air to do it rather than having to press down on the analogue stick.
...of coarse a fully customizeable button mapping control scheme option would be best if 343 can do it.
Grenades I think that the damage/blast radius for grenades is perfect, so leave it be! I also like how they kinda push you back a good bit when they go off.
Shields: Shields felt just a bit too weak here. I get that people don't want to have to shoot a bajillion bullets to kill someone, but I found that I was dying a lot faster than in previous halo games...It felt a lot more similar to Destiny which is OK i guess, but I personally would prefer just a little bit more shield health.
Sniper Rifle: Scoping on the sniper takes too long. They need to speed it up!!
Mele: The melee animation was too slow (or maybe it was imput lagg?) When I press the melee button I want it to feel instant!
Overall though these are really small things, and I really like the new direction 343 has taken. The graphics are also what I expect from a Halo game, and I think if they can just get it up to 1080p or 900p with good AA then I will be happy!!