Mine are:
(Ranked)
1. GTA Series
2. NFS Shift
3. Silent Hill Series
4. Pac-man (Lol)
5. Tomb Raider Series
Pac Man, yes! I am shocked I forgot to mention that!
Even Ghost Recon: Advanced Warfighter 2! Hard-ass game.
I forgot to mention Contra, men I can't even get through the first level. Plus Battletoads from my Sega days, this was painstakingly addictive and difficult.
You are keeping me reminded of the good old days where games were the most difficult to beat.
Mentioning Contra, which is indeed difficult, I am reminded of some more games too!
F1 Racing (Boy I used to get ****ed when the car used to hit an obstacle and used to get exploded).
Pepsiman: This product motivated game was fun, but was very, very challenging.
Race Driver GRID: Sluggish handling makes the game difficult. It was impossible for me during the earlier stages to come first.
Tetris, easiest in the earlier stages, but the most challenging on the later stages.