Hey, I bought a copy of your album a few months ago and I was wondering how many copies you made and if you used a lossless audio file when burning it. Your music is really awesome btw, it's a shame more people don't know about it.
Then that's perfect because out of all of those PC and Xbox 360 have the most new exclusives, and more of the first time ports. There is a very cheap trilogy available called Raiden Fighters Aces as well as Raiden 4. If you are will to shop on a site like Play Asia and HMV, you can hunt down Mushihimesama Futari (Bug Princess 2), ESPGaluda 2, Eschatos, and the EUROPEAN release of DoDonPachi Resurrection. Xbox Live Arcade has Strania, Orbitron, and quite a few others. All exclusive on the platform...unless you own an iPhone which the bolded games are available for.
That depends on what sub genre you like. The two most popular are Danmaku (bullet Hell) and basic. Neither genre is harder. It really depends on the game and don't let anyone tell you different.
What I can recommend for each sub genre that isn't too absurdly brutal, but still a challenge would be Akai Katana (Bullet Hell: XBox 360) and Thunder Force 4 (Sega Genesis).
I can give you better examples, but I also want to name what's easiest to get. Your PC will run any shooter guaranteed so what systems do you own?