Shooters are cool. My favorites are R-Type and Layer Section. Although I think R-Type should be faster, while Layer Section should be more difficult. But they're cool because their gameplay is different.
Layer Section still has the best sprite effects ever.
http://www.the-underdogs.org/game.php?name=RayForce
Kenta Cho's shooters are all about speed, though.
http://www.asahi-net.or.jp/~cs8k-cyu/index_e.html Tumiki Fighters has an interesting concept.
I still remember playing SWIV. I loved it when I was a kid because of the overkill powerups, though I've only beaten the game once. The intro and stage 1 music is still in my head ^_^
But meh. People like different things:
- Higher difficulty (though some like it easier ^_^)
- Powerups and varying gameplay
- Faster/slower gameplay
- Flood the screen with bullets (*cough* Kenta Cho)
- etc.
A cute'em up is a good break from the space theme, though. Marchen Adventure Cotton 100%, Keio Flying Squadron (I wanna play this one ^_^), etc.