I enjoyed it, but there are a few issues:
1) Nyreen is in your party for like...10 minutes total. She's really not around enough for me to feel anything about her.
2) The content is overall really freakin' easy. I was playing as my shotgun infiltrator (it's as close as Mass Effect gets to a backstabbing rogue. Just instead of stealthing behind someone and backstabbing them, you sneak up and blast them in the back), which is pretty OP I admit. And Aria is just a beast. Her Flare ability wrecks shit. It's that "Biotic artillery strike" we've been hearing about. It's fun as hell to use, but it really just makes this whole content a cakewalk.
I can't say much for Nyreen's abilities. She has some shield that she can cast on herself, but it makes her unable to move or shoot. So it's a tanking ability, but the DLC is so easy that tanking is totally unneeded.
However, I did like quite a bit. I like Aria as a character. She's like Mass Effect's version of The Duke of New York (Isaac Hayes' character in Escape from New York). Something about that kind of character is really fun to me. And as OP as she is, her abilities are fun (in addition to Flare, she has a Lash ablity that acts as sort of a Biotic whip. And she has Carnage and Reave). I like how they handle the main villain at the end. I like Omega in general (it just has that 80-early 90's cyberpunk vibe that I like a lot). I like the contrast between Aria and Nyreen. And I like the idea of one of the new enemy types, even if they aren't so intimidating in practice.
On another note, did anyone else level up a ton doing this? On my new playthrough, I started up Omega basically as soon as I could, so I was about level 37 or so when I started. I leveled up at least seven times, maybe more. Seems like they were dishing out a ton of XP.