It has some pretty good gameplay and also some very funny dialogue. Overall the game was quite enjoyable and varied, with the player able to play three unique individuals during the SP campaign.
However the third act of the game is a little lackluster to be honest. It lacks the witty dialogue from the previous 2 acts and the action itself is a little misplaced. It feels like a bit of a cop out, story-wise, to enable the 3rd perspective. The story itself doesn't take itself that seriously of course, but it could've been handled a little better.
The RTS elements I thought were also a little problematic. The resource gathering can get a little tedious, and worst of all if you die you respawn with your base intact but the enemy threat level diminished. The RTS scenarios are typically such that the opponent steadily attacks the player with greater and greater forces, but when the player dies the computer goes back to square one and attacks with minimal amounts again. Also the battles themselves are a little bland, would've been nice to see a few more varied elements involved. The Reapers for example have more variety than is represented in the RTS battles.
Most of the boss battles were pretty easy as well. Though that's typical of many games.
On the whole, it was pretty good and worth the six bucks if nothing else.