Fallout 3

After Operation: Anchorage and The Pitt's failure to launch, Fallout 3: Broken Steel is a breath of fresh air.  With the extension of the main quest, new level cap, perks, weapons, side quests, and new areas to explore, Broken Steel adds over 10 hours of gameplay that will give you a reason to return to the capital wasteland. 
 
For those who completed the main quest and discovered that there was no playing past the end will be pleasantly surprised because to access this content after you have downloaded this DLC, all you have to do is load a previous save and complete the final quest again, and instead of seeing the credits roll, your character will awaken inside the Brotherhood of Steel Citadel two weeks after the events of the final quest.  It is here where take up arms with the Brotherhood and begin your campaign to rid the capital wasteland of the remaining forces of the Enclave. 
 
Throughout this new questline you will meet new characters, kill enclave soldiers, and be introduced to new enemies, such as the super mutant overlord and the feral ghoul reaver.  Both of these new enemy types are powerful and a pain in the ass to kill but this adds more of a challenge to the game. 
 
For those who buy this for the xbox 360 will have six new achievements to unlock, three for reaching level 30 with good, bad, or neutral kharma and three for completing the three new quests in the main questline.  These quests will have you fighting alongside liberty prime, finding resources necessary for new weapons, and ultimately taking the fight to the enclave in one final epic battle that leads to the grand finale of the Fallout 3 quest.  Each of these quests are very challenging and will most likely not be completed on the first attempt. 
 
If you are interested in purchasing DLC for Fallout 3 and you can only get one, then I highly recommend this be the add-on you invest your money in.