Ok, put some more time into Top Hunter with a friend. This game is a very fun, but feels a bit sloppy at times. The background/foreground thing is pretty cool. There are a few parts where you need to jump back and forth to solve a mini puzzle. However, it isn't always clear what is in the background and what is in the foreground because the size difference between the two planes isn't different enough.
There are lots of power-ups and things to collect, but I haven't really figured out what it all does yet (again, feels a little sloppy/loose). There are 4 "worlds" with 3 stages each. The end of each stage has a boss. I found the final bosses interesting, but again, the jumping back and forth between the background and foreground was a bit confusing.
So far I have played through 2 of the worlds with a friend, and one of the worlds on my own. I will plow through the game one of these days, preferably with a partner.
Oh yeah, did I mention this game is gorgeous?