the game is really good when you get the hang of it. It's not generic at all. The story is distinguished mentally-challenged, but the core gameplay is a damn good shooter. Not Vanquish or anything, but still high-quality mechanic shooter. The upgrade system rocks.
Anyone who likes good Japanese mechanic action games like Shinobi or Vanquish should play through it. And yeah there are more than two enemy types. Each stage introduces new enemies after the first chapter or two. There aren't a lot but it's about learning how to fight each one. Game is a good challenge, not cheap hard, but fun challenging. Stage 3's camera in a couple of the big open areas is kind of bad though.