By far? Well I personally would go so far as to say they were the worst raids. I disliked DS and Tot4W (yes it's still a raid with 2 bosses, so was gruul), but definitely not putting these as the worst, I actually enjoyed HFC. The unique mechanics for 20 was kind of a loss though since the only boss that really had a unique mechanic to change your roster was furnace and the use of priest mc's. 20 man I think was actually a decent success, although I kind of like larger raid sizes so saying goodbye to 25 man sucked, but so far this new raid size has been great. Also your argument for wiping mechanics... doesn't that really just apply to raiding as a whole?
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It's unfortunate that you personally had to deal with the drawbacks of 20 man raiding when it was released with your guild falling apart, and that's most likely why you think it was a complete failure, but how could you not think it is a good idea. Sure nothing is perfect, but it killed the annoying 10 vs 25 debate by allowing them to balance a challenging mode to apply to all raiders. Most guilds that are 10 man and have been for awhile had to adapt and recruit, and if they couldn't, then they were left in the dust, but honestly if you refuse to keep at it to play the difficulty you want then you shouldn't be getting it (said broadly, not pointing you out).