So Dead Money was Fallout's take on survival horror, Honest Hearts was straightforward wilderness adventure, and Old World Blues was an especially awesome and often hilarious dose of retro sci-fi horror, Lonesome Road follows as Fallout's take on... a dungeon crawl.
And don't get me wrong, as a dungeon crawl, Lonesome Road is exceptionally well designed. You have dark dank tunnels to run through, traps to disarm, phat l00t to find, undead and constructs and aberrations to fight, and a big bad who taunts you through magic messages. That the "dungeon" is a devastated military facility and nearby town, and one exceptionally built at that, is just fabulous. If I were to set out to build a dungeon crawl game and I made it similar to Lonesome Road, I'd have done a great job.
But Lonesome Road is also supposed to be the essential finale to the Fallout New Vegas story. Sure, we all know the actual end to the story is the end to the main game (all of the DLC stories take place before the story's end). But if we played the game plus DLC in order of release, Lonesome Road is last. It's the big shabang everything was leading up to. The Big Bad gets name dropped early on in the main game, and most of the DLC all mention Ulysses and/or the Divide and the Courier's inevitable showdown involving that man and that place. For months, the hype has been built: what's going to happen at the Divide is going to be mind-blowing, reveal-all, amazing.
And instead of a mind blowing finale, we get a dungeon crawl.
The story is a loose blob of cryptic messages that strings together your purpose for traveling through the maze of twisty passages, all alike. There's only one human person in the story, and his sole purpose is to taunt you so that you remain annoyed enough to traverse the Divide so you can shoot him in the face before he sets off a nuclear missile strike (which he could have done without inviting you for the show). And that's it. You don't learn very much--Honest Hearts gave better insight both to the history of the Legion and important characters in New Vegas's backstory as well as shed light on life at the edge of the apocalypse. And it's easy to miss a lot of the clues there are. I found them, but it still doesn't fill in many blanks, and in some cases just leaves open more questions and seeming discrepancies (for example, Ulysses seems to imply the Courier accidentally wrecked the Divide, but evidence you find suggests it's always been an unlivable hellhole ever since an earthquake went off before the Great War started).
Ultimately, because the story is both piecemeal and contradictory, the point of playing through Lonesome Road feels much less like bringing history to a close and revealing more about the Courier, and more like an excuse to go hunting deathclaws in a post-apocalyptic ruin. And there is absolutely nothing wrong with hunting deathclaws in a post-apocalyptic ruin, but it shouldn't have been marketed as anything more than that, and it shouldn't have been the finale.
Purely gameplay wise, Lonesome Road is solid. The environments are exceptionally well built--there are a lot of toppled buildings and you have a lot of freedom of exploration (with minimal risk of falling through the infrastructure like Fallout world design tends to incur). If you're the kind of person who plays Fallout mostly for the shooter aspects of the game, you'll love Lonesome Road--fantastic areas to go hunting monsters in. I'd say Lonesome Road is even most enjoyable when you ignore Ulysses' ramblings and just explore and kill things.
I did experience some memory/slow down issues (on a brand new computer), although some of those were resolved after a graphics driver update. So make sure you're up to date on everything before you play. I didn't encounter many gameplay bugs.
The mechanical add ons are a mixed bag. There's a handful new weapons and armor, and you'll be very happy in particular if you like heavy weapons (my pistol toting light armored sneaky gal had less to make use of). There are several crafting recipes I wished I had about 30 levels ago, and there are several perks I'd wished I'd been able to build my character up to (there are notable exceptions in the form of a set of perks only available at level 50, which are very cool perks at that). This further makes Lonesome Road frustrating as a capstone piece--most of what it has is great for low-mid-level characters, but it's a high level adventure that came out when most who've bought it first have played through the game and are going to use their highest level characters to play through it. I seldom do multiple playthroughs, although Fallout New Vegas in general has high replay value, so I imagine the most I will get out of Lonesome Road is not the adventure itself, but the perks (literal and figurative) it will offer to new characters.
Oh yes, of course, there's also ED-E. You encounter a similar eyebot and can upgrade him (of course, by the time you finish upgrading him, you lose him). Any upgrading you do to Lonesome Road's ED-E transfers over to your companion back in the Mojave, if of course you weren't one of the people, like me, who had him randomly disappear in the middle of the Wasteland and never come back. I guess it's cool to get ED-E's backstory, but to me he'll always be a floating bucket of bugs more than anything else, and being a floating bucket of bugs with extra perks isn't much better. I'm also a very character-driven RPG player and I prefer the humanoid companions anyway. And on that note, frustratingly, ED-E also gets a perk which makes Veronica's workbench perk redundant (I guess maybe it's fair because Veronica also gets an "upgrade" perk from Dead Money... or it would be if her bonus perk applied to her actual preferred mode of combat).
In summary: the designers deserve a lot of credit for environment design and providing a lot of opportunity for both action and exploration (something which is hard to balance). Gameplay add-ons are a decent touch. But story and character-wise, Lonesome Road is far and away the weakest of the Fallout New Vegas installments. If you play the game for the story, you can skip it without losing much. Honest Hearts was a less bland foray into adventuring and had more main-game plot relevant. Dead Money was much more tense and terrifying, and Old World Blues was far more entertaining with an infinitely better set of antagonists. If you can only afford one DLC, make Lonesome Road your lowest priority. If you have all the DLC or are planning to get the Ultimate Edition in February, play Lonesome Road as soon as you can (which is still not until level 25) and save the better DLCs for later.