My beta impressions: I dont like 4 vs 4. Its limiting and lacking all the epic, team-based gameplay of the Big Team battles. Slayer is nothing new and the breakout gametype is boring. All the best MP games these days excel the most at unique objective-based game play and that is lacking here.
The powers arent anything new either and have already been around since the early days of Crysis and most recently in COD: AW. Also the character buidling and perks (other than new armor) that really build addictive gameplay seem to be lacking (I realize its a beta). I really hope that with the graphics boosts the game is planned to get (it does look really good) that 343 isnt sacrificing the big team battle aspects that makes these games so fun to play in a team work based PTFO style environment! - My 2 cents! Thanks for listening 343!