Well, personally I loved Lonesome Road and I think it was the best DLC. The first time I played it I didn't appreciate the western-like style of New Vegas, so seeing the Divide's nuclear horror filled some void. I kind of missed the post apocalyptic theme in the game.
But yes, there were a few shortcomings, to say the least. Let me put them in a list:
1. Tunnelers - annoying and overpowered, I always die at least once on that elevator.
2. Scripted Deathclaw encounters - while I learned to sneak my way and take them down, it was hard in the beginning to take them by surprise. Not to mention NV Deathclaws are a real deal, especially the irradiated ones.
3. Warheads - the very idea was kind of silly. Oh well, still a better nuclear story than Fallout 3. Also, they were conveniant when there were Marked Men around.
4. Ulysses talking style - oh my, riddles and metaphors! One hour in the game his talking gets boring and annoying. Bear Bull Old World Bear Bull Courier.
5. Ulysses as a character - I liked him, but I still find him incomplete as a character. Basically, he makes his attitude towards the Courier as a revenge, but claims it's not a revenge after all. He seems like he hates you, nope, denies that too. Bashes you for siding with any side, yet believes America will rise from the ashes of the post-post nuclear world, after he burns California and Four States to the crisp. I have a theory that Ulysses is so disillusioned and disappointed with the world that he retreated to his own imaginary world of old world America, which reflection he found in that community in the Divide before the missiles launched, and that losing this community pushed him even deeper into the, at least partial, insanity.
Still, Lonesome Road is my favourite DLC. Despite its flaws, I enjoyed almost every moment of it.