@ above poster: Um, maybe that's where YOU saw it, but I can assure you that ET didn't invent the red "critical health" feature. Otherwise I agree with you, because right now there isn't much contract between the hp lettering and HUD background, so it's hard to see your health peripherally. And having to take your eyes off that goon just to see how much damage he did is not a good thing. I'd propose something like this:
90 to 100 hp: green font. Means "dude, you have over 90 hp, don't worry"
60 to 89 hp: regular blue font. Means "you took a hit, but you're still ok"
30 to 59 hp: yellow font. Means "Uh oh."
1 to 29 hp: red font. Means "OMFG RUUUUUN!!!!"
That way you can just see the colour with your peripheral vision and know what your health situation is like much faster.
Another suggestion, simply for aesthetic purposes, would be to have your hp slowly pulse while a medkit or medipad is healing you. Just the sort of thing where the colour goes whiter, fades back to normal, goes whiter, fades back, etc etc.
@original poster: yeah, it's already been mentioned several times. I still agree with it completely though, I remember someone having to tell me that when I first started playing, and it gets annoying when EVERY new player has to ask a question like that. And yes, I DID read the manual first, but I guess it's an easy part to forget. Aaaaand finally, it's just an extra mouse click that accomplishes nothing, because you ALWAYS have to sell before you buy a new gun.