WoWDB

Sunken Temple - a.k.a. The Temple of Atal'Hakkar a.k.a. Lost Temple - was much bigger and grander prior to Cataclysm, as is seen in this detailed (and semi-obsolete) image of the dungeon zone.

Copy-pasta from Wowpedia because why not.

All floors below the top and the bosses they contained have been removed. Upon pressing a snake statues in the Pit of Refuse in the proper order, the dire troll boss Atal'alarion spawned in the middle of the pit. In order to kill Jammal'an, you had first to kill Gasher, Hukku, Loro, Mijan, Zolo, and Zul'Lor, who were standing on the six ledges overlooking the Pit of Sacrifice. Once all six are dead, the shield protecting Jammal'an faded, and he was reachable.

Although I didn't like the instance when traveling through it with a LFD group, I did like the immersive experience while soloing it - the story and the artwork, primarily.  Now the instance is indeed much shorter and easier... but it also became much more boring.  Not to mention the pang of deep sorrow in my soul when transmogrification was added to the game and I realized that those removed bosses dropped items with unique models.

The younger generation of WoW players really missed out on some great stuff.

Here is a list of loot that includes the removed loot drops.