I'd also like to add Flywrench and Jill Off to the list of games that make me happy, but cause no end of screaming at my computer and embarrassing myself in front of my room mates.
Man I have the demo of Ikaruga on XBLA, it is quality but so hard if you're not used to it. Does it get easier? Or do you still find it banshee-wailingly hard?
Ikaruga is hard, but it's so much fun! It beats you up 99% of the time, but when you get a new high score you feel like you're the second coming of Christ.
And don't worry, once you learn the stages, they become a lot less difficult. And the flipping gimmick becomes second nature. If you want to get better, the practice modes that let you replay a specific section you're working on. Also:
http://www.super-play.co.uk/has some inspirational gameplay videos.