I got bored with SP pretty quick. I haven't even finished it. MP, on the other hand, is quite enjoyable. Playing as the marines kind of bores me (personal taste, probably), but it sure is fun playing as the xenomorphs and trying to get the hang of them. I like the customization options for them too, although I haven't unlocked much yet. All-in-all, it sure was disappointing after all the hype the game was given, but I still am enjoying it. The MP. It'll be a lot better soon as they fix the bugs.
I personally believe there could be a MP Alien game that has the proper feel of the movies instead of a more basic shooter game. It just needs to be done right. For instance, the environment would need to be darker and harder to see in. For the marines, anyway. The maps would need to be a lot more closed-in, so the marines can't go out in the open and wait for the xenomorphs to come out at them so they could easily gun them down. This is especially true for outdoor maps. There would need to be a lot more nooks and crannies for the xenomorphs to crawl through, so they could sneak up on the marines. It just needs to be done so that the people playing the xenomorphs can rely on stealth to defeat the marines, and the marines feel a sense of dread and need to be constantly vigilant. And the xenomorphs should outnumber the marines in versus mode, instead of having even teams.