4400. They could have gone on, but I was cool with where it ended. The genie was out of the bottle.
The genie was not out of the bottle. The discovery of ubiquinone means that the government now has a way to prevent the spread of promicin, while permitting the creation of promicin-powered soldiers safely. The stakes were ratcheted up, yes, but the conclusion left completely in air. Also, we still had no information whatsoever on whether Jordan was right, or about how the timeline could be altered.
Now and Again had a definitive and logically satisfying conclusion, which is that the hero and his family were all captured and killed offscreen, by the Dennis Haysbert character, who was carefully portrayed as murderous.
Alphas also had a finale which can clearly be read as conclusively finished by the deaths of the majority of the cast. As I recall, only autistic Gary survived. Naturally, he would be returned to prison without Rosen's custody. This too is logically satisfying. It is survival of the characters that would be a stretch.
PS As noted above, Sanctuary had a very well-done open ending. Wish it had gone on.