Aye, I've tried it. Pretty much completed most content in it too (up to Malygos 25, hopefully clearing that this week). I personally feel WoW got a serious improvement with Wotlk - the lore in the quests make much more sense than they used to (you don't collect 20 quests anymore and do them all at the same time; you follow long questlines with good stories instead).
Also, the new "phasing" allows for some very interesting things, such as zones actually changing when you do quests in them (i.e helping a faction clear out a bunch of undead in a certain place, allowing the faction to put up flight paths, vendors and quests in that zone instead of the undead being there).
The music is also a lot better than it used to be, especially in zones like Howling Fjord (as Essaliad mentioned, this is a great zone to start out in).
The biggest feature is obviously the Death Knight class. Very solid. Almost too solid. Not only does the class have very fun, fast paced gameplay - it's also extremely powerful. The only drawback is that so many are making one: They're everywhere now (yes, even a lot running around in level 80 instances already).