Ok, awsome might be an understament for the improvement in Halos multiplayer... Ive play most of the the grab bag modes, btu mostly slayer and the most rewarding thing to happen is an assinate kill, like really having a mini scene rippiping somones back apart = pure awsome!.
For those who don't know how to obtained the beta, get a copy of odst campaign disk and click play the beta takes an hour or so to download though so make sure you have time.
Once you login i suggest starting off playign slayer to get used to the new control scheme, which is my main scheme forhalo :D. The right bumper melee is super easy and the left bumper item use is much more convient then the colored buttons in my opinon. But ok the scout is for sprinting, pick up a energy sword or gravity hammer and sprint to an enemy then melee for kill. the guard i havent seen much cool stuff from except killing them. i highly enjoy watching them guard then right before it end throwing a grenade so when it ends they die. the stalker is by far my favorite, rouges on halo? yes sir! best was to get the awsome looking assassinate kills for sure crouching and sneaking up to a back and stab stab stab away. i absolutly love it. the airborne is my second favorite, taking a rilfe and flying to a high point that only other airbornes can get 2 and picking them off one by one. honestly it doesnt feel like halo anymore, but much more awsome i cant wait to see how the real multiplay pans out. the new guns are pretty sick too, the needle rifle = holy crap awsome. there is also this thing that locks on and shoots blue balls at an enemy(dont look at guns names sorry :/) but if ur not careful u explode too. the only other gun i like is the new start out gun, its a lot better and more fun and i can kill pretty well it so hunting for a gun isnt asnessicary but ones with scopes are still better.
overall the beta is worth playing and odst is down the35ish dollars used so why not??