Very nice, I love the style you've used here, looks almost like an animated series.
Now, going along the lineup: I like the salarian, he looks very, well scientific. He seems to be missing the bulging chest strap thingies most salarians have, but that might just be his style. Finally, he just doesn't feel original to me, more like a younger version of Mordin.
I love what you did with the quarian, her suit design is very nice. Better looking than Tali's ME1 garb, or the generic quarian outfit, but still definitely not tali. You got her knees right too! Almost no quarian fanart gets the knees right. However, the mask visor looks too large and convex. Could be because it's stylized, but it feels off to me.
Nice fem!turian. (she IS a she, right?) She looks feminine, without loosing the predatory, horrible-spiny-monster appeal of Garrus. If anything, I'd say she looks more predatory. Not so sure about her color scheme though, seems turians prefer either C-sec blue, or some red-and-black or brown combination.
The drell seems like the generic everyman. Not the smartest of the bunch, but good at heart. (At least that's what I get from his face). I like how his outfit is rather simple, but still detailed enough to fit into ME cannon. That said, boots and the leggings between his shorts and the aforementioned boots could use some work, they just look a little bland.
The Asari looks, like, she's from, like, the valley. Her face gives her a, like, airheaded, like, image. (now I'll stop that) You posed her well, and I like her boots. Her whole outfit seems very athletic. Tennis players come to mind. However, her top seems very skimpy, and I doubt a little strap like that would do much in the way of support or reducing bounce-age. (though that may be your goal)
I have to say the krogan is my favorite of the bunch. Sleeveless krogan are always win, and yours is no exception. His face is great as well, cartoony enough to fit with the style, but still mean and blunt enough to be krogan. His pose as well is really fitting. The only negative thing I can think to say is the red ring around his right arm seems to overlap the opening for his head. (right at the very top). It's pretty pedantic, but it kinda annoyed me.
Finally, the Vorcha. It's funny that cartoonized like this, even he looks (very slightly) cute. His face specially looks d'aww worthy. The texture on his skill doesn't look very vorcha-ish, and I recall vorcha as having much longer, pointier teeth.
So I didn't want to blather on with a full critique, but I wanted to just say a few things!
First - I love it! I think the idea is great, the design and quality is great! Fantastic!
The Drell and Quarian look a bit too generic to me. If you had someone seeing this who was only vaguely familiar with the Mass Effect universe, they might think it was Tali or Thane or cause some confusion.