I would like to preface this recommendation with the following comment: Due to the similar and short nature of the Quantum Conundrum DLCs (about 2 hours per), I will be writing only one review for both. With that said, let's get down to the nitty-gritty!
For those who've beaten the core game, you may be disappointed to learn that none of the DLCs will expand on the abrupt ending. There's no indication of when and where these extra puzzles take place, but that doesn't detract from the quality of the content.
The Desmond Debacle and IKE-aramba each offer six new levels (twelve total) that will rigorously test the player's creativity, reaction, and patience. Each puzzle typically starts with three or four powers already unlocked, widening the player's options on how to tackle any given obstacle. Because the game is now less direct, it's also a bit harder.
Monetarily, you could be doing a whole lot worse than $3 for six new and challenging levels. This here is DLC done right.