Well so far I've played OWB through twice. First time with a new character (got there Level 4 finished Level 19) and second time with my high level explorer character (in at Level 37 finshed at Level 42).

Upsides
-A lot of love for the Proton and Protonic Inversal Axes. I was able to do about 80% of the fights using Melee even when, on the new character, I didn't have any points in it.
-An excellent new player house
-A decent story line (if you don't mind Fallout 2 style tongue in cheek humor)
-Some interesting new traits/perks.
-A few pieces of good equipment.

Downsides
-No one handed version of the Proton Axe;).
-While the story is decent I never really care about any of the characters the way I did for the ones in Honest Hearts. Hopefully Lonesome Roads will get back to that level of story telling.
-This is just peronal taste admittedly but I'm not a big fan of dungeons/bunkers and OWB is nothing but bunkers. The outdoors between them is pretty much just there to slow you down on the way to the next bunker.
-Two of the quests require you to go through the same bunker multiple times to get the maximum reward. I know there are limitations to how many areas you can pack into a DLC but that's just lazy level design and monotonous.
-The Thin Red Paste and Blood Sausage from the "Them's Good Eating" perk can come from humanoids as well as animals. Sorry but I just get the mental vision of some developer doing a Beavis and Butthead laugh while saying "Finally getting these a-holes to eat people".
-The Logan's Loophole trait completely removes a major game dynamic, addiction, from the game. But that's personal taste and I don't have to choose it if I don't want to.
-All though I already put the player house as an upside I'd also say it has it's downsides as it really dumbs down a lot of gameplay featues that are there to keep the game halfway challenging. Salient Green means no more exploring for rare ingredients to make the high powered foods, and the Toaster/Book Chute/Mugsy means rare components are commonplace. Again, I don't have to use them if I don't want to, but it's a bit annoying they spent so much time on these features and neglected level design.

Bottom Line
Not the best DLC for me but mostly because I enjoyed Honest Hearts so much and my expectations were high. Also most of my complaints were about features most players will find a God send so by all means buy it if you like the gameplay changes I mentioned. Otherwise I'd say wait for it to come out in the inevitable Game of the Year Collection