Broken Steel lets you play forever,but I think that Mothership Zeta is better.
Operation Anchorage it's really practical, gives an Invunerable Winterized T51-b with 45 DT, and the Gauss Rifle. Best taken early on as it provides top qaulity gear and power armor training.
The Pitt's a goat fuck, avoid it. Point Lookout's a bit monotonous, I prefer the others.
I'd take Broken Steel, if only one, BS and Operation Anchorage if two, BS, OA, and Mothership Zeta if three, BS, OA, MZ, and Point Lookout if four, I've only purchased The Pitt as I bought Game Of The Year edition and it came along.
Personally broken steel is the best one ive played, and i have bought and played all of them).
- Point Lookout is a new map which you can travel to, which is set in the swamps. It's full of killer rednecks and crazy hillbilly treasur hunter motherf@#$ers. There's plenty of locations and side quests to keep you busy.
- Mothership Zeta is about the Lone Wanderer being abducted by aliens, and must work alongside the rest of the captives to escape. It's very linear with only the main quests to complete. But gives you a lot of good, valuable gear, such as Paulson's Revolver (Non-Scoped .44 Magnum) and the Winterized Paramedic Combat Armor/Helmet
- The Pitt is about an escaped slave asking you to help him rescue his fellow slaves from a large gang of raiders. You travel to Pittsburgh and decide if you want to save the slaves or help the raiders. It's horrible, the environment sucks, you're pretty much naked out there, but when you beat it you get good guns. Like the Infiltrator.
- Broken Steel adds extra missions onto the end of the story, and it's about the Brotherhood of Steel killing the last of the Enclave. Raises your level cap and lets you play after the story ends.
- Operation Anchorage lets you travel back in time through a simulation, where you fight the Chinese on the Alaskan Front Line before the Great War. Very linear with no side quests. But trains you in estrategic use of comapnions and diferent types of gear. And unlocks a few of the best gear in Fallout 3.