I played a couple matches, on one Deathmatch server as a Pulse Rifle'd Marine, and a Species Deathmatch as a Predator Only things I can report so far:
1) I did sometimes get an error message about it being unable to connect to a match, then tried again and finally got through.
2) During the Predator match, the map I believe was called the Subway (it has tall buildings to stand on, some street level and, yes, subway tunnels), I jumped off a building and briefly got stuck on the side of a building. All I could do was look around as I was dangling in midair until a few seconds later I finally dropped down. Not a big deal, but I'm trying to be as thorough as I can.
I haven't tried out the Alien yet. I'll be doing that next time I boot this up.