First of all, I'd like to say that this DLC is way better than Leviathan. It took me roughly 4 hours to beat on Insanity. With that said:
Story: The plot's bare bones, but it does make some helpful additions, mostly by making Cerberus's sudden power jump from 2
make something resembling sense. A lot of people will probably be dismayed that the end result has no effect on the main plot, but I don't mind it. There are very few choices, but there are two very powerful scenes that are probably the highlight of the DLC, both of which involve interrupts.
Characters: Aria gets fleshed out a lot more. Nyreen is a good character, and her dynamic with Aria was entertaining, which makes it all the weirder that she's lazily written out near the end. Petrovsky doesn't get a lot of screentime but is an effective Chessmaster and Anti Villain
, and a foil to Aria.
Gameplay Additions: The best addition to the game is, by far, the Adjutants. They're a ton of fun to fight and possess capabilities that make them unique, such as their "Singularity Gun". Rampart Mechs are also nice. The problem is that there are maybe a dozen Adjutants in the whole DLC. This is a shame, since they were a good challenge and interesting to fight. That's the general problem with this DLC and all Mass Effect DLC: it's short. There's also a few weapon mods and two new guns. Base gameplay is mostly the same, though I noticed that the level design was much better, with shield pylons and cover being placed in ways that make you think. You also get two new squadmates and two new powers; both squadmates are incredibly fun to use, especially Aria.
Other: I like the general feel. The urban warfare, the entrenched enemies, the zombie apocalypse, etc. I also like the way the story is set up; specifically, makes the battles we're fighting make sense. There's a reason we're doing this. Mass Effect 3 had many moments where I wondered "why the hell am I shooting zombies behind chest high walls when sentient ships are wrecking the galaxy?". Omega doesn't have that.
Final Verdict: 7.5/10. If you love Mass Effect and can't get enough, go ahead and buy it. However, if you like to conserve your money or are still waiting out on a DLC that has an effect on the main story, just keep your fifteen bucks and let Cerberus and Aria squabble over this slum-filled rock.