I think I'm around 60-70 keychains last I checked. I love collecting them! I don't know why...something really satisfying about them. The Sun Stones are pretty easy to get, but since they unlock the boss stage, it makes sense haha. So far, I've 100%'d the first four worlds. Working on just getting through the 5th one and then I'll go back at some point and work on 100%ing it. I went back to the other worlds before I started the 5th one, though I mean...I was only missing like...two stones per world, so that's not bad at all, really.
Overall though, I'm still really enjoying this game. The level design is fun and creative and I really enjoy the puzzle solving with the rockets and cannons with the fuses that you have to light.