I  just bought Dr. Zed's Zombie Island (or however it is titled) and the Underdome DLC add-on today. 
I've only gotten to play through the first one, Dr. Zed's, but I really enjoyed it.
I really enjoyed the tone, atmosphere and presentation of this add-on. While I didn't find myself scared or anything or threatened to go around a corner I really enjoyed the creepiness of the whole level. I really dug the choice in colors, the forestry and the old American Haunted house look of the buildings throughout the level. I liked the little touches of the jack-o-lanterns as well if I was a kid I would have felt a little more threatened. The only thing I could hope for would be that they could've made the maps a little bit more darker but it is a comic styled game so the brightness kept that flavor intact and didn't detach itself away from the vanilla title. The music was pretty good it really kind of captured the whole idea of being alone (for the most part) pretty well. 
 
I'll start the Underdome tomorrow.
 
What are your thoughts on these Borderlands DLCs? Like em? Hate em? Why?

In my opinion, of the 4 DLC's (Ned, Moxxi, Knoxx, and Claptrap) Ned is by far the best. It's whole creepy "Night of the Living Dead" feel that makes it so great. Being the first DLC it proved with it's humor and in-game content that it could stand on it's own legs just a well as the core game could. Ned really does kind of have something for everyone in terms of finding something they can love about it. Moxxi isn't that great. KNOXX is a -huge- DLC with a lot of content but lacking fast travel makes it a pain in the ass and Claptrap is pretty damn entertaining. Hopefully you'll enjoy them all before too long. Cheers mate.

I loved Ned's. I'm a sucker for the whole halloween, horror theme going on. I just started the Moxxi DLC. I put  the game off for a little to play some other games and I'm sort of disappointed with this DLC. It's just sort of boring I guess and the fact that I don't earn EXP for kills or get my weapons leveled up either sort of erks me with the difficulty in the waves sometimes. I don't think I'll even really give a real attempt at trying the 20 rounds of 5 waves version of the arenas. I already did the regular versions. So I suppose I'll have to wait until I can buy another MS points card to try out the next too but they seem to be a lot better than the Underdome.