Fills in backstory and adds good mechanics
In the SP campaign, having three races that are balanced in respect to each other even in different environments is surprising. For instance, inside buildings the alien is at an advantage which is balanced by more marines to take out. The Pred's overwhelming abilities are balanced by not being an elite Pred till the end of the game. The marine is compensated for being weak by a fairly effective arsenal....all of this is a long way to say that all the fights seemed fair and consistent with the race's abilities.
And on that, while in AvP original you get some sketchy outline of the race and how they relate to their opponents, there's enough in AvP 2010 to flesh out some details, which once again seem consistent with the AvPvH world as portrayed in movies and games to this point.
Finally, on tension, while it's not as scary as the original was in 2009 (and nothing will probably ever be given its ground thats not been covered), there are plenty of adrenalin surges play as any race when you realize you've overlooked some detail (headcrab, turret gun, hidden predator) that is about to kill you.