In Assimilation, you'll have to battle Borg opponents with other pals, since the AI bot teammates can't really go through the complicated task of blasting them while avoiding capture. Elimination takes out an opponent for the rest of the match if they're killed, making for an instant tournament. Disintegration puts a compression gun in your hands that allows you an instant kill, making for a variant on the Rocket Arena. Because Specialties is a type of game rather than an entire mod, the full effect of having special team member with certain skills isn't as drastic as when you're playing a game designed around those concepts like Team Fortress. It's a nice addition though.
Assimilation is more entertaining in concept than in action, unfortunately.
New characters to choose from add to the multiplayer list as well, including the fun robot and other black and white characters from the Captain Proton universe. The multiplayer definitely couldn't stand alone as an expansion to Elite Force, and yet it's the most thought out feature by far of the new ones available. Unless you're a devoted fan of the show, or are still playing multiplayer Elite Force to death, I'd have to say no. The crowd of you out there that bought the original because it was a great shooter that also took place in the Star Trek universe are going to be disappointed, and overall, all of you are going to be disappointed in the lack of the stuff that made the original so great. This isn't so much an add-on as it is a completely different sort of game altogether, one that's simple and straightforward enough to make you antsy for the original again.