I like the concept of platformer arena shooter and I've always liked the concept "The Floor is Lava".
A few things I would address (just as recommendations, of course):
The Lava is not very dangerous because of the ability to jump. It sounds silly, but I think you should be able to gain more momentum when grounded - it creates that notion that it's hot and you want out.
The game's pacing is a little slow, which may be due to the size of the arena or lack of ability to get around unharmed. The game is a pseudo-platformer, but there aren't always good paths to take (or any at times).
Tidy up that little bit and I think people will have even more fun! Keep up the good work!