Let's put it this way: the mutons are naked.
It's more of an arcade game where all you do is go running about with your finger pressing down on the fire key and blasting away hundreds of aliens at a time, grabbing "power ups", blowing up alien transporters, grabbing civilians or perhaps killing the occasional boss. Oh, and you have to suffer listening to the voice of the professor who really should spend more time building another enforcer rather than making overly enthusiastic, corny and completely unnecessary exclamations while you're doing what you were built for.
It falls short in so many aspects that it feels incomplete in some way. If you've played games like Dues Ex or System Shock, then this is nowhere near that level of sophistication. It could have been done better. Despite the numerous complaints I'd like to make about it, I must admit, it can keep you amused for a while.
I'd recommend getting it just for fun. But if you want a seriously engaging game -- this is not for you.
If you have a choice, try grabbing Slave Zero, which was also published by Infogrames (back when they were still called Inforgrames, anyway). It should be in the bargain bins, along with Enforcer by now. It's a bit more polished and you can at least choose to pick up your old weapon if you ran over one you did not want. Also, it allows proper aiming with mouse-look. Very important, IMHO.
P. S: Regarding mouse-look, if you get Enforcer: do not turn it on. The camera angle does not follow the aiming reticule. This makes it very difficult for precision aiming. Just let the auto-aiming do its work for you, and you'll be much happier.
Makes it an incredible chore to admire the landscape and look at the various signs though.
NKF, wordmakeupper extraordinaire.