Last time we saw John Shappard, Elizabeth Weir, Teyla, Aiden Ford, and Rodney McKay, the lost city of the Ancients was under a severe attack from the Wraith armada, with very little hope in the promise of reinforcements being their only chance for survival. As an attempt to stave off the Hive ships, John goes for a suicide mission, armed with a nuke...but fortunately the cliffhanger is resolved in an action-packed 3rd parter, and sets up the basis for a whole new season that sets the groundwork for things to come.
The characters and the mythology behind the Pegasus galaxy are developed even further, especially in regards to the Wraith (Which makes things a little less black and white than it is in season 1). Some things even take a darker tone as the team committs actions which may be seen as foolish and immoral, and taking this fine line makes the situations far more dynamic and interesting.
The episodes range from great to outstanding to okay on most occassions, save 'The Tower' which is an ep you should watch only one, due to terrible writing the story falls flat in that one sadly, but is made up for incredibly quickly.
As for extras, the discs are chocked full of the damn stuff! No need to worry there. On the whole, buy, watch and enjoy another great sci-fi season.