When I first played the game it reminded me of the "Fireboy & Watergirl" series ("The Forest Temple" and "The Light Temple"). Was Zombie Crypt somehow inspired by them? I won't consider it less original if it is, it's just curiosity.
I played and beat the game with a friend. We had a great time but here are some suggestions if you're going to make a sequel:
1) Show some instructions to introduce elements (if you play F&W you'll see
what I mean).
2) Fix the hitboxes (I could say it's the game's biggest flaw).
3) I think you should remove the gold pieces and make the levels more challenging so that the point isn't to pick up stuff and get to the exit, but to have fun playing through the levels.
4) Make more death animations: it's a bit weird that everything explodes regardless on how it dies.
5) What every sequel must have: more elements, levels and stuff.
Some things you SOULDN'T do in the sequel:
A) Checkpoints: the levels are short enough. If you lose, in less than 5 minutes you'll be where you died the previous time.
B) Create a story: these kind of games aren't supposed to have a deep story, they're just supposed to be fun to play. You can create a story about 2 friends who have fun killing zombies in caves if you want to, but then you'll have to explain why there are levers, button and circular saw blades everywhere.
C) Change the graphics: GO RETRO!
Hope this helps you to make a Zombie Crypt 2. Keep up the good work!