I played this game as soon as it was uploaded to Newgrounds. I read the instructions first, so I wasn't shocked that there were rooms with reversed controls. It certainly speaks well of your programming skills and potential as a game maker that you listened to the feedback in the reviews to tweak a few things that were frustrating for some players, like putting reverse controls in enormous letters in the appropriate rooms.
I thought the game was really well-designed. I like the graphics well enough, nothing was garish or off-putting as far as visual appeal goes. The music has a nice beat, but the sfx are a little too tinny sounding, even for this type of game. The blowback effect is a bit strong, but that's your choice as creator. Since you've changed the instakill spikes and lava into an 'hp burn' effect, the blowback is just another element of gameplay. I agree with your assessment that adding health isn't necessary because the game's premise is 'how long can you survive'.
The only improvements I would recommend besides a sfx tweak would be more variety among enemies and perhaps a toggle to adjust music and sfx volume, not just 'on' or 'off'. If you ultimately decide to add health to the game, I would limit it to an unlockable 'gauntlet' mode where there is no ceiling for numbers of rooms cleared (a player could conceivably clear hundreds of rooms in that format).
Great job, I look forward to more submissions from you.