SO WHAT THE FUCK
I want this to be a thread where people introduce new action games to others as well as discuss favorites. It's a pretty broad term, and a lot of genres are covered - shmups, run-and-gun, platforming, &c. It would also be nice if you could upload or link to the game.
Alien Soldier, or This Game is FUCKED after Level 17 (Genesis)

http://rapidshare.de/files/6657938/Alie ... _.bin.html
I firmly believe that this is one of the best games ever created. Great controls, music, and graphics. Crazy difficult, but it can be overcome. I can basically breeze through up until the boat scene with the teddy bear and then things start to get tough. I can't beat the huge eagle. Haven't found a practical application for the fixed shot, and I think that's part of what's holding me back from mastery - the comfort level I have with the weapons and stance I use. LOL @ joker frog.
Abuse (PC)


http://www.webpages.uidaho.edu/~scot4875/
So many lesser-known fantastic action games on the PC. This is one of my favorites. I love this game. It's like a muddier, more visceral contra with superhuman abilities. The muddiness is also a downside, some levels seem repetitive. The main website is down, but I just found a pretty good site that might have everything you need. More and more information on Abuse is being lost and that's sad.