Serious? Ulduar was my favourite instance of all time. That place was crisp and tuned wonderfully. Hard mode Mimiron, Freya, 0 Light Yogg and Algalon were probably the best encounters they ever designed I reckon. TOGC Immortal was pretty freaking cool too - Anub'arak 25 HM required so much precision from every single person in the raid - it's a shame most attempts were ruined by the stupid "PvP" encounter. The only other fight that ever compared before that was Illidan in TBC, and nothing afterwards came close - although Atramedes (sp?) was a very clever design.
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