Ok, so playing through it slowly, but it really isn't filling me with desire. It isn't all bad though, it certainly isn't "Game Over man, it's Game Over!"...
The Marine Missions (so far, I'm about 30% through) are TERRIFYING. Atmospheric, dark, tense, and the motion tracker is a sound that haunts me to this day from my childhood. The introductory missions are good, and provide a real build-up to just how powerful the Aliens can be, and how reluctant you should feel about fighting them.
The other two though, I'm less keen on. I've tried them both, and whilst the Alien missions are interesting at the start, you feel so underpowered. Same with the Predator, you just don't feel like a bad-ass.
I'm currently not hating it, and am keen to continue, but it's not wowing me. I hope it does.