Though there has been a lot of great content through the years Warcraft has had it's share of completely crappy content. With the release of Cata there is one instance that makes me cringe every time I go into it, Throne of the Tides. For some reason my computer hates that instance. Whenever there is someone who has something on them that makes their character not fully appear that toon is under the ground on my screen. Being a Goblin whenever I am in Camo this happens and my Ghost Wolf also appears under the ground. The puddles of slime that appear with some mobs are also under the ground which makes it hard to see them because I can only see the top part bubbling. Even with completely upgrading my computer and making sure my video drivers are updated I still have this problem.
With the older instances it would have to be Blackwing Lair. I dont mind the instance as a whole. It is the first boss fight that I hate. Razorgore is so buggy that it seems like the raid stops before it even starts half the time. Grumble and I went in there last week to try to duo the instance but we couldn't get control of the orb for the fight. After about 45 seconds we would explode. After looking up the fight on WoWHead we learned there is another bug that makes the raid die instantly once the mind control over Razorgore ends. It just seems like a terrible fight to start off a great instance. I would like to run it weekly but hate the repair bills because of no fault of our own.