Assault on Dark Athena is totally worth it. It’s like three games in one (Butcher Bay Director’s Cut, Assault on Dark Athena and the MP) and Butcher Bay is one of the most rewarding gaming experiences I’ve ever had. This game is the definition of a top notch game. The atmosphere is perfect, the dialogue is badass, the levels are interesting, the game is challenging, and the characters are really defined. If anything, you are buying one game and getting two for free, and I cannot stress this enough, if you have not played Butcher Bay before, you MUST buy this game. Like now. Do it.
I have not been able to play the MP or the Dark Athena campaign yet. But that should not stop you from taking a look.