I really do have to agree with the majority here.
The campaign mode is awful as some levels are nearly impossible, the story line does kind of fit with the TV series but that's about all that is good about it. The voice over from all of the captains is a nice touch though. With only like 3 missions for each captain they could have expanded on that, and that i found to be a really let down.
The skirmish does redeem Star Trek Legacy slightly though. It has a good replay value to occasionally go back to, but i'm sure with the difficult controls it would get frustrating after a while. The graphically explosions on most of the ships are very good with a nice boom created, but on the Borg large ships the explosions are awful with the ship breaking apart dreadfully. There are some catastrophic errors in the game as well where your ship flies through other blowing up ships and bouncing off the wrongly proportioned planets. The controls are quite difficult to get a hang of and to master them is unfeasible.
Overall i believe that if your a really Trekkie then you'll probably love it and if not then you will just get frustrated by a lot of the bad failures.