It's a good idea trying other tilesets, as the Epic sets have been used to death and you will probably end up creating places you've seen in the original game.

For creativity, of course it can be difficult, but it's not as hard as most people think.

For example, try to do something well known the other way around. I've seen invisible tiles which could be shot to get platforms, instead of blocks which can be shot to clear a passage. Everythings possible.

You can also try thinking about what you can do with events and what you can't. For example, the floating sucker event. It's normally used as an enemy. In FSP: Rent Collection they were used to make glowing floor, which hurts the player.

Of course I believe you put hard work into your stuff, it's just that you seem to neglect some important parts.