CoD 4 demo out
 

From various sources; I got it from Boomtown.

Looks terrific. I just got a new widescreen monitor, and with my new system the thing is really good.

Pretty much the same sort of CoD gameplay everyone is used to; no medics, but you can absorb a lot of small-arms fire, then you have to go hide for a few minutes to regain health. (not much on the realism factor here, but that's how they do it.)
Just as in previous efforts, you get killed by grenades a lot. Same little "grenade warning" icon.
Nice mix of contemporary weapons; in the demo I saw the typical range of US and foreign stuff you'd expect. M-16s, AKs, SAWs, RPGs, etc.
Effects on the enemy were pretty much one-shot one-kill with the rifles.

Be interesting to see if the multiplayer is improved in the full game. Thing looks so good....