Painkiller is a fun game, great graphics - tons of secrets too - you can blow through and shoot everything in sight and just try to find the next level/exit, but you miss out on quite a bit if you do that - and the AI is significantly improved with some of the recent patches - the boss characters are tons of fun too. Also, Painkiller DOES NOT use the Crytek engine.
Guys, not to anger anyone, but I played STALKER at E3, and other than the sniper weapon, I wasn't impressed at all - it was multiplayer, and although the weather effects were wonderful - they had the time greatly accelerated, so the sun would set every few minutes, which was a cool effect, but I was really let down - the single player looked great in the demo room, but I think the jury is still out on this one.
No retail chain has their Doom 3 copies already - your buddy may be looking at the pre-buy boxes or some promo material, but they don't have the real thing yet. Good friends of mine are software buyers for two of the largest retail companies in North America - and there is simply no truth in your buddies' claims.
I'm not going to get into the Doom3 vs HL2 thing - if you aren't anxiously awaiting both games, then you really aren't a fan of the genre - there are quite possibly the two biggest PC game releases of all time!
Finally, the clown that said Halo 2 looks better than D3? Maybe if you are comparing the X-Box versions side by side, but trust me when I tell you that the excitement around the Doom 3 launch has little to do with the X-box version.