Seems like its gonna be kinda dull...the whole locking on aspect of MP might cause it to get boring. At least with other fps theres a little more skill involved with aiming and whatnot.
A friend of mine played it at a conference and pretty much said exactly what i was thinking...after 5 minutes everyone playing got bored, rolled up into balls, and just started smashing eachother. While that sounds pretty funny, I also think it's more of a bonus and won't even compare to the single player experience.