Minerva's Den is my favorite piece of DLC from this gen. Highlights:
- It tells a great little self-contained, ultra-focused story with a perfect ending
- It delves into the philosophy of artificial intelligence with a lucidity uncommon to games
- Two primary characters have diametrically opposing views on the subject and comment on it in intriguing ways throughout the game, and Porter's musings in particular are always enjoyable to listen to, and often touching
- It's well-paced and doesn't wear out its welcome
- Its combat is more immediately and consistently enjoyable as you get access to a wide variety of plasmids, tonics, and weapons early on, and the new toys and baddies are fun
It's ideal DLC. Taken as a whole I think it's more successful in its execution than the main Bioshock games. Similarly to some of the better New Vegas DLC like Old World Blues, the devs used the idea of post-release content to take a stab at doing something strange and creative with an existing setting, and it worked beautifully.