Very good, if not basic
Sometimes basic is good, though. You've got everything a flash game really needs: this can be picked up and played for a minute or two, there's a clear goal, and it has easy to understand mechanics. What you have here is the very core of what makes a good game, but the problem is that you didn't expand on that.
A little bit of depth never hurt anyone, even if it was something as simple as unlocking extra characters for endless mode whenever you earn an achievement, it would have been appreciated. I'm not saying to implement a whole points system and a shop or anything, but it's the little touches that make something truly great, and while this game is built well, it lacks polish. The sound follows the same ideal as well. Now, I'm not saying that this kind of music can't ever be good (see the Final Boss theme from Crash Twinsanity), but for somebody who's trying to get their sealegs in endless mode, I can see how it would start to grate on someone after a while.
All in all, this is a nice little time-occupier. I can't call you out on anything you did; just the things you didn't do, which is where you want to be. However, something can feel quick AND deep at the same time. It's not easy to achieve, but I'll be looking forward to your next piece of work, and I hope to see what I'm looking for there.
