Yeah.. well, I didn't really have much direction when making this one, there was just some time left in the jam and I thought I might be able to squeeze another game in there.
I was thinking something like this when making it:
Top down, Hero Core (another game made by someone I can't remember), slight metroidvania elements (upgrades / secrets).
So reminding you of Metroid is not that far off as that was one of my thoughts when making it. ^^
And if you don't finish the game before the green circle runs out then you loose the game, assuming this is what you meant by "life bubble".
Anyway, thanks for playing. :)