Totally worth it. Completion isn't to far off as long as you keep in mind how to play and communicate with other players for the MM stuff.
The story is pretty much what you would expect with this sort of setting, its hard to have something totally original when there is already so much done in the setting and similar settings like it. But there are no weird plot holes or weird explanations for tasks, nothing that leaves you confused as to what is going on.
I honestly feel the graphics are appropriate for the game, voice work is exactly what I would expect from the setting. My only beef is with the vengeance launcher, rather pointless weapon.
Anyway, yes, get the game. Even if you don't play the MM, you can still enjoy the story and get a lot of the achievements solo.