I enjoyed the resource balance you have to do where you have to spend life to attack, but doing so obviously makes you more vulernable. It's also nice that it regenerates, letting you switch between offence and defence in a very dynamic way.
Some death indication or level complete indication would have been nice to have. There were too many instances where I'm not sure if I beat the last enemy on a screen or it killed me, as the transistion screen looks the same in both instances (and it didn't help that the green guy somehow kept killing me even though it died?)