Like the weighty animations, the engine (apart from when it causes immense flickering when passing by leaves, planks, anything with a lot of lines), the ultimately rather fast paced combat, the leniency for cast-tail movement, and that healers and tanks can both do significant DPS dependent on their coordination with each other and the raid's present pace).
Not a fan of the oversights (Skill/Spell Speed, Diadem, original PotD), rapid content obsoletion, lack of core innovation, how animations rarely do what they look like they should do (see single-target Spinning Slash), how the fast pace is really just a product of every job being identically GCD-locked with a backing arsenal of oGCDs, the singularity of optimal rotations, or the shortage of cross-role responsibilities (especially for DPS party members) or versatility.
[Not saying I want every roll to be able to heal or tank, but they should have a way of getting around or restoring damage, whether that be by kiting, killing, swapping off, or whatever else. No one should 99% of the time be concerned only with their parse, or in addition only to minimizing their own raid-damage taken). I'd like to see more abnormal compositions, more alternate ways of approaching a given problem or encounter. And yet we're mired instead in CC immunities, etc.]