1 - Devidians - loved the TOS parts, and the "bonnie-kins" episode which was brilliant. Never understood why my ship from the future (with the hologram hiding it) could pound the historic ships to dust in seconds.
2 - Reman/Romulan - some interesting story telling, if not always brilliantly designed missions.
3 - Breen - while I enjoyed some of the missions, and the breen as an enemy, the puzzles were awful and the Deferei a very badly thought out species.
4 - Dominion - should have been brilliant, but the early missions just put me to sleep. As above, hate having to repeat missions to get the full set - they're boring enough doing them with your different toons without having to do them more than once with each toon.