Demon's Souls
Why? Here it goes:
-Diablo2(hell) / Dmc4(DMD) feeling is back...(difficulty lvl)
-Co-op... if you are lucky to have a friend :P
-DS is a new form of testing your rage control... like no others i know
-It's painfull yet rewarding
-Demons/Skelotons/Dragons even "Death" with its minions...not to mention sadistic bosses.
-Atmosphere - you know you are going to die soon.
(Others on my favorites list are: Dragon Age,Oblivion,probably FF13(started playing today) )
Cheers from Norway :D