Recycled art and environments - 2 bosses were in maw pits from Highlands, 1 boss was outside dragonblight tower, 1 boss was on ICC boat, 1 boss was in EoE tower, and final fight happened at the maelstrom. On top of that there were very few new boss models or skins.
Lack of themed and meaningful trash - properly done and paced trash helps make a raid feel unified. ICC and Ulduar trash were both good examples of this. The trash also lends a good pace to progression and allows you to feel like you're working through a dungeon. DS lacked this - the best trash in the instance were the colored blobs that (theoretically) gave you insight into the bosses abilities, but even they were just crap in a circle. If they had removed the dragons and teleports and then provided thin trash packs you fought through on your way to the maws and then up the tower it would have been far better. The dragon trash before Ultra also felt useless as it wasn't skippable, always lasted about the same amount of time, and didn't give you any connection to the upcoming boss.
Over reliance on add style fights - the last three battles of the instance are add based. While add based fights can be a nice change of pace in a raid, making just shy of half the raid be add fights was anticlimatic and made three bosses feel much like glorified trash.
Disconnected and repetitive fights rather than multistaged fights for an expansion ending boss - Illidan had 5 stages with at least two of them being distinctly different from the others, The Lich King was 5 stages with 3 distinctive phases and 2 transition stages, Deathwing was spine (rinse and repeat 1 phase 3 times) and madness (rinse and repeat 1 stage 4 times followed by a burn phase with more adds). This means that both Deathwing fights combined had less stages than either previous expansion end boss and fewer stages than most dungeon end bosses from any of the expansions.
Poor difficulty balancing - LFR was a joke, everyone knew it would be a joke, but the fact that you could ignore all the mechanics was just sad and set an expectation for future LFRs that is detrimental to player development and to recruitment for guilds as it does nothing to help the guild recruitment pool, rather it floods the pool with poorly skilled, overgeared, and over confident "raiders". Normal modes were also terribly balanced (even casual guilds cleared normal modes within a week or two). Hard modes (especially on things like spine) were over tuned. Very little felt appropriately balanced.
Very few bosses for a raid tier, let alone an end raid tier - TBC had BT + MH (14 total bosses), Wrath had ICC (12 bosses), DS had 8. This was combined with Cataclysm's overall lack of content (FL and DS combined had roughly the same amount of content as Karazahn or Ulduar alone).
Then trying to stretch that content over 8 months . . . .
What reasons are there for DS not to rank?
---------- Post added 2012-12-05 at 11:47 AM ----------
I disagree with you on Sunwell, but you have good reasons of your own, so each to their own.
I just wanted to comment on the idea of 8 bosses per tier.
Tier 1 - MC and Ony (10 bosses)
Tier 2 - BWL (8 bosses)
Tier 2.5 - AQ40 (9 bosses)
Tier 3 - Naxx 40 (15 bosses)
Tier 4 - Karazahn, Gruul, Mag (14 bosses)
Tier 5 - SSC and TK (10 bosses)
Tier 6 - BT and MH (14 bosses)
Tier 7 - Naxx25, EoE, OS (17 bosses)
Tier 8 - Ulduar (14 bosses)
Tier 9 - ToGC (5 bosses)
Tier 10 - ICC (12 bosses)
Tier 11 - Tot4W, BWD, BoT (13 bosses)
Tier 12 - FL (7 bosses)
Tier 13 - DS (8 bosses)
There is a strong argument for your case and the common perception agreeing which perhaps is also tied to the idea that only 20% of bosses will be better than average. The more bosses a tier has, the more likely it is to have one of those memorable bosses and thus for the tier on a whole to be remembered fondly. For example, TK wasn't great and SSC was also relatively average, but because of Vashj and Kael that tier tends to be very fondly remembered. Same goes for MC - the tier and environment are nothing special, but the Ragnaros fight was so memorable that it adds value to the whole tier.