Where do I start....
*Final Fantasy VIII: "The Omega Weapon", by the time I reached Ultimecia's Castle I was level 100, all round pretty much, I had the "Ultimate Weapons" for each character, powerful spells, the best GF's and all the limit breaks, there was no real strategy back then that would allow you to defeat the Omega Weapon, it was so insanely powerful, even for an FF Optional Boss, I remember using a Gameshark, even that didn't work, If you managed to survive its first onslaught of "Meteor" and "Terra Break", hit it with Meltdown and then Lionheart a 1/3rd of its Health away, it would still come back and pretty much wipe your entire party out with another "Terra Break", sure I could complete the game, but the Omega Weapon is a must do for any player of the game, even if your only awarded with a silly tutorial page and an Item you won't need if your that powerful enough already to attempt to take it on
*Star Trek: Legacy: "The Meteorite Mission", goes without saying, I gave up on the game after this as it was just insanely difficult, that along with the glitches, barely responsive controls and repetitive gameplay ruined what seemed like an excellent game
*Tekken Series: Later Titles: Ok so I appreciate a challenging game, but the Later Bosses in the Tekken series are just insanely difficult, even for experienced players, you cannot throw them, combos usually get broken up mid way through, they block absolutely everything, can quickly get multiple attacks in, they juggle you always and to top it off, when you've beaten them, you still can't unlock them to use!!
*"Ladder Matches" In The Smackdown Vs Raw Series: Seriously a match that you cannot win against the AI, unless you resort to an underhand tactic, such as taking all the ladders and running to the end of the ramp, to trick them, thats just a really badly thought out AI
*Online Multiplayer Exploits: Goes without saying, people who play Online are either Good, Bad or Cheaters and more often than not they find ways to exploit the game, such as in FPS' like the Call Of Duty series or people who play the game solely to try and make a profit in most Online RPG games, where the overall gameplay becomes about finding Rare Items and offering them for money to other players
I think that about covers it for now!