I don't think it matters how you get health back really, so long as the game is built around it for balance.
In the end no game where you get damaged is remotely realistic. Imagine a game where if you die it locks itself and you can't play it ever again - that's realistic. Or you have to spend two weeks waiting for your character to recover from a wound - that's realistic.
In the end I do prefer there is a reason for whatever health option is taken - and I do find CoD4 etc the oddest simply because reg seems to fit the game setting the least - but it's not a big thing either.
Halo 1, Resistance, Half Life each probably struck me as having the best reasons for their choices:
Regen in Resistance due to your Chimea infection
Halo 1 - basic health with rechargeable shields
Half Life - health and energy stations dotted around on walls in a sensible manner
In the end regen is popular, I believe, because its fast and allows for frenetic gameplay with no need to find health packs, etc. It also makes things (IMHO) a little easier - but that might be the bitter old PC player inside me thinking all console based devices (which regen seems to be) are in aid of making things easier and faster and less complex.
In the end I just take the view the only way I'd ever get through any of these games if they were real was if I never actually got hit - and in some ways regen does give that feeling better than finding health packs.
Try to be reasonable... its easier than you think...
