I checked it out.
Firstly, the download is a bit big. 260MB which unzips to over half a gigabyte!
This is ridiculous for a game like this (unless there's a huge amount of content later in the game which I didn't see). Is the music uncompressed .wav?
Controls don't work properly with my 360 controller - left stick movement is OK, but moving the right stick left and right shoots up and down respectively and I can't shoot left or right.
As for the gameplay - it feels pretty solid and I can see the potential, but in its current form I got bored pretty quickly. The monsters drift around randomly so it's easy to just strafe at the sides of the screen and mop up some hearts every now and then. Without any kind of homing behaviour or basic AI it doesn't feel like there's much in the way of challenge.
Staying alive by refilling the energy is a really nice idea - but the UI should communicate my current energy level more clearly, like with a big bar along the top or bottom of the screen, or use a bigger font to display the value and change the text colour through yellow/orange/red as it decreases.
Graphics for the player, monsters and items are all great, but the background could do with a little bit of colour and variation.