Built on the universe developed in the other Stargate series, SG-U is simply the deepest one in terms of the gravity of the story and the weight of the characters (the performance of Robert Carlyle is particularly great). The fact the cast has many young actors infuses new blood into the franchise. It felt very realistic to me, and I loved the shroud of mystery that permeated everything, almost like the same style of Battlestar Galactica.
Though the first season was a bit loose, I can't blame them as the new series was just trying to figure out itself, like a teenager. But then it bloomed into an awesome second season that was unlike any other SG series before.
It is an utter shame that it was cancelled. Hopefully, with the advent of streaming services, MGM (or Netflix) might bring it back to life. It's most definitely worth a shot!