I did not factor Broken Steel nor GRA into any of this. If anyone has some they wish to point out or correct me on, feel free.
Operation Ancourage and Dead Money:
A lot of people hate this DLC. Have everything taken away during the main part of the DLC. New restrictions are placed on you in this new location. This new world is quite a site to behold. At the end you fight the main boss/talk him down and talk to the person whose been giving you orders this whole time. Also they both are Brotherhood related and has a Vault of goodies for you with some DLC only stuff.
The Pitt and Honest Hearts:
To get to the DLC you have to go north and meet up with someone contacting you via their radio call. He'll help you get to the location. This world is very different from the base game. The main leader of this new area was a major member of one of the main factions you can fight for in the base game. He has unique armor and a good voice actor. You have to make a major choice between two people and their wants and both have good and bad consequences. Good writing went into this DLC but it is sorta on the short side.
Point Lookout and Old World Blues:
To get to the DLC you must go to a south point on the map. This new region is dark and full of dangerous new enemies. Some of the most enjoyable humor and quests comes from this DLC. You end up at one point talking to a disembodied brain and surgery is done involving your brain. You can reunite with your brain near the end of the DLC. There is a twist on who the major villian/villians really are. There is a new player home for you to use.
Mothership Zeta and Lonesome Road
This DLC is hated by many. You have a character who unlocks things for you. The first person you meet in this DLC has previously worked for an evil faction. You see part of the world get destroyed by a large weapon. You can later destroy the part of the world if you choose to. The final quest has many waves of the main enemy of the DLC.
Some of these can be considered stretches and of course some depend on how you play. I've been curious about the similarities awhile, especially with the brains with the 3rd, vaults of the 1st and the 2nd being short. Point Lookout and Old World Blues are the most popular of the DLCs as well.