It is actually a good time. Plays like L4D2 with aliens instead of zombies. Gunplay, turrets, barracades, all kinds of goodies,.. even better playing w/ buddies.
There are a few different game modes also - regular story lines gameplay , a horde-type waves of aliens, etc...
The only thing really missing is the characters/ banter are not as interesting as in L4D. ( which is admittedly a high bar to actually achieve though )