I've got the first boss to where I want it and I've made some changes to the HUD.
The orangey-red blocks under the time meter act as a progress meter, with one slot for each stage and each boss. This is meant to give the player a better sense of where they are in the game, and to up the tension (i.e., I've got three slots left but I'm down to my last minute!).
You'll also note some numbers on the bottom of the screen; this is how much you've scored from destroying a given enemy. The game doesn't actually keep track of a numerical score; killing enemies really just fills up the XP bar in the upper right. But I want to cement the idea that killing certain enemies fill up that bar faster than others, and that doing so when the multiplier (between the two bars at the top of the screen) is higher will do so even faster. Just looking at the bar might not do the trick; a higher number is easier for players to grasp.
Onto the game's first boss, or "god":
I'm not going to say much about the above, other than the obvious: as the player depletes the boss's health bar (which doubles for the XP bar) and blows off chunks of its armor, it starts doing different sorts of attacks. It's possible, I've found, to beat the first boss in roughly ten seconds, and indeed the secret to doing so is revealed in one of the above screen-shots.
It's also possible, however, for this battle to last the better part of two minutes-- not the best turn of events for the player, given the game's over-all three minute time limit. This is due to the system that's been put in place of death in this game; taking damage in the multiple enemy stages will deplete your XP meter, while taking damage in a boss fight will increase the boss's health meter. I think this actually ups the stakes more than the traditional "get hit and you die" or extra lives system.