My first impression is -- graphics are beautiful but the game itself is deadly boring.
Essentially, you use counterintuitive keyboard controls to make a starship fly like a biplane and keep hitting the mouse keys until a meter (representing the enemy ship) turns completely red. That's the combat system. I'd rank it considerably less interesting than Pacman or Pong.
There's no strategy to weapon selection. Every time you touch the mouse it meaninglessly changes the camera angle, which has no connection whatsoever to your ability to fight. So your point of view is always jumping around, for no good reason. You could just keep your hand off the mouse, but then you can't fire. I imagine that some customization of the controls might have fixed this, but the fact that they'd make such a crappy set of default controls argues poorly for the game design.
While you're fighting, the "aliens" keep making stupid remarks like "The Praetor wants you dead" -- as if that's supposed to add some drama to an essentially pointless exercise. If you manage to get close to the enemy and get the enemy in your forward sights, you get a better hit. That's an excellent strategy for a Sopwith Camel, but completely archaic for a starship. Moreover, as the ships get bigger, they get slower and duller. Great design concept, guys.
If I were to net it out, I'd say that Legacy takes the dumbest part of Bridge Commander (the mind-bendingly dull combat system) and combined with the dumbest part of Starfleet Command (the limited "combat area" concept) and rolled it together with a dumbed-down version of Microsoft Flight Simulator. It really doesn't get much worse than this. Seriously.
In short, as a game, Legacy is a real dog. The graphics are gorgeous, though, so it will probably be, like Bridge Commander, primarily useful as a machinima engine.