>>720276837
All three are standalone, launched from the main menu as self contained experiences.
Desperate Measures is straight up cut content repackaged as DLC. It's short, not terribly exciting and there's literally only one way to get the "good" ending where you learn what you went to find out.
System Rift is set in a new area of Prague and a new, kind of dull office building. Pritchard's in it. It's alright but it connects to an event in the main story that's completely unimportant.
Criminal Past is set in an aug supermax, a story that takes place before the events of the game and completely unrelated to them but told after the main game is over. The longest and best one if you're willing to put in the time and effort.