Okay so:
It is a 2003-2007 FPS Windows PC game.
It had graphics that were something like CoD1/CoD2 but were not better than CoD4.
Kinda dark atmosphere,not totally dark but definitely not cartoony/funny/.
Combat was somewhat wave-based,but I am not 100% about that.
It is definitely obscure,its not something popular like CoD/MoH/Rainbow Six series.
I played the demo only,and i remember one unique thing:you could turn your enemies into Santas and Nutcracker soldiers via options or something.
I also remember that one map from the demo,it was pretty small,approx. 2 times smaller than Dust 2 on CS,i know there was a building with an open door and there was some food on the table there and you could eat it to regain a small amount of health.
I guess that the game was multiplayer-oriented but I played it offline so it probably has some kind of campaign.
It had old guns,nothing sci-fi or modern,no full-automatic guns IIRC.
Thanks in advance :*