I have recently been introduced to PAINKILLER.
There is also PainKiller : Battle Out Of Hell to go for when you have completed PainKiller.
What do I think of this game?
Well, take every game that you have ever found to be better than any other game, and throw them in the bin. This baby is far far better than anythign I have ever had... Except a couple. ( UT / Quake2 )
I can only fault it on one thing, and even that is debateable... AI
Everythign else is beyond brilliant... GamePlay, Massive number of levels, fast frantic gameplay, absolutely perfect physyics, tons of bad guys, coupled with puzzle-elements, and scary too! - makes Doom3 and Ravenholm look like a sunny day in the park.