what was the first ever Rated M game you played?

For me:

Conker's Bad Fur Day :D

Perfect Dark.

Halo or Halo 2 I believe, back in like 2006.

Mortal Kombat on the Genesis. I don't think there was an ESRB back then so it wasn't technically "M", but it did have a 17+ sticker on it.

Resident Evil 4 on the Gamecube. AH-mazing.

Probably Mortal Combat when I was a kid. Used to have nightmares of the levels where you could kick a guy in front a train or into a pool of acid and see his bones afloat. ;)

Halo 1.

It wasn't rated M, but Zombies Ate My Neighbors gave me nightmares more than any other game I've ever played; so it kind of worked as if it were my first M :P

Mortal Kombat 4.

diablo

Halo 1