lol question :-/ hard is a relative term here. Instead, u could have picked up a Hardcore, or Really Difficult game(but single one) and then put this question up.
This is just like this one: http://www.hltv.org/forum/145579-who-wins
Painkiller - Heaven got a hitman (Trauma)
Painkiller - Battle out of hell (Trauma)
CoD and CoD United Offensive (Veteran)
CS CZ Deleted Scenes
Medal of Honor - Alied Assault & Spearhead
IGI 2 - Covert Strike (Agent , IGI Agent and David Jones) all of them in 100% in some maps my accuracy was 90%+ to get the David Jones rank)
GTA Vice City and Worms 3D // SKill levels are in the missions 1st missions/maps easy last ones pretty hard especially in worms:D
I got 3 stars (by myself, except the ones where you needed to play with 2 players) on all the special ops missions on modern warfare 2 on my friends PS3 @ college. Damn those were addicting. A lot curses were thrown at that poor ps3.