To help prospective buyers decide which are worth picking up and which ones aren't, IGN has profiled and ranked all five of Fallout 3's DLC packs. On the "definite" pile, you'll find Broken Steel and Point Lookout. On the "maybe try this" pile, there's The Pitt. And then we have Operation: Anchorage and Mothership Zeta sitting atop the "for the hardcore only" pile.
There's really only one thing you need to know about Broken Steel. By buying this add-on, the level cap is lifted another 10 levels to 30. Anybody that has played a lot of Fallout 3 knows that you'll hit the original level cap long before you've seen and done everything. With Broken Steel, you get to continue gaining experience, improving your skills, and unlocking perks.
Of course, we wouldn't recommend buying Broken Steel if all it offered was a lift in the level cap. This download also enables you to continue your game beyond the ending. Simply finish the game after installing Broken Steel and you'll find the game continues with this new storyline.