999 is one of the best games I've ever played. The ending is fenomenal and that's all I'll say about it. Do note that it's basically a visual novel with puzzles and that it requires a lot of text skipping, as you'll need to replay the game multiple times to really finish it. It's worth it, though.
I've been thinking about going for the Massacre route this time around in Apocalypse. I don't think I will, though. I still find it impossible to be a complete asshole to anyone in a video game, unless they somehow deserve it. I couldn't play full renegade in Mass Effect either, for example.