Dynamite Jack is the bomb.
As I said before there are limited enemies but each of them behave remarkably different from each other. Collecting crystals improves your time on the speed run leaderboards that exist for every map including user made maps. The ability to easily create new maps and share them with the community is the real gem of this game. It is going to drastically improve the life of this game.
This game is good value if you enjoy this type of thing. If you get addicted to playing or start making your own maps then $5 bucks will be a steal.