It's extremely buggy, there are no animations for anything (so you just see a bunch of combine floating around). You can only pick up stuff for the first minute or so, so pick up everything while you can. When a person dies, their body stays in the air and they respawn, so it's hard to tell when you killed someone. Oh, and drowning crashes the server...so when you want the server to reset so you can pick up weapons, just drown. Oh, and you can't chat, so you'll be expressing yourself through jumps. Also note that there is NO master serverlist so you will not get any servers by searching.
Yes, its far from amazing or perfectly working but do note that the full Half-Life 2 SDK has not been released yet and there is, as of now, no official HL2 Multiplayer so, be content