My priest is level 43 now, and already did his first expedition to Uldaman. And I don't really like that place. The difference in level between the start and the end is too big, and even with the backdoor you can't really advance directly to the end. So either you go with a lower level group, have fun in the first half and then get beaten to pulp in the latter part, with the final boss fight being simply impossible. Or you go with a group able to beat the final boss, and then you have to kill lots of mobs that are far too easy for you.
I prefer places which are either linear, but with not so much of an increase of difficulty from start to finish, like Shadowfang Keep for example. Or places where the easier and more difficult parts have different entrances, like Scarlet Monastery. It is a lot more satisfying to form a group able to beat the whole dungeon in one go, without being bored at the earlier parts.
The additional problem with Uldaman is the main quest, where you first have to go to find the shattered necklace, then go back to the city, go again to Uldaman to find the paladin, then go back to the city, then go back to Uldaman for the 3 gems, then go back to the city, before you get the final quest for the final boss. As most people have to rely on pickup groups in this level range, and pickup groups always disband when going back to the city, you need to find a lot of groups for Uldaman to do that main quest. I find that annoying, especially since Uldaman isn't a very popular dungeon, and it isn't that easy to gather a pickup group for there.
What I do like is the story that is told in Uldaman, which gives you a lot of background on the history of the creation of Azeroth, and the Makers. I just wished the game flow was smoother there.