Great story. Skills & Dialogue centric-add on.
There are three types of basic enemy. The holograms which cant be attacked. The ghosts roaming the villa which are hard until you work out what the best way to down them is and the red cloud, which is there to restrict your movement and hurt you periodically.
Where I felt the Dead Money excels at is the story. Its intriguing, imaginative, well written and narrated. The setting is also fantastic, really giving you a sense of the foreboding events that would have taken place there. These also give the characters of this long forgotten place a real edge so you start to empathize with what would have been their plight. The way it uses 3 NPCs to get you through the story and combat is an added bonus. Keeping things fresh by changing the perspectives of each of these very difference NPCs.
Im not a great fan of artificially handicapping players in games, but removing all the players equipment and making them scavenge for what they can find really helped in making you want to explore every part of the map as well forcing to to treat every item with great care, in case you don't find another item again. Unlike in the main game which lacks a fair amount of gameplay balance. DM is much more a leveling playing field.
Perhaps though, its best moment is perhaps the final battle with Elijah, where you have two choice with how you determine how you end the game. And a very satisfying ending it has.
SPOILERS:
Attempted on level 35. Made it to level 40. Combat was very, very tough at the beginning, as the standard weapons are useless.
Best attempted with high stealth, melee, unarmed and speech.