there are three categories of mass effect alien design that gives the setting its vibes.
the first and by far largest is animalistic. not in the sense of anthropomorphized animals, but in the sense of extrapolating the aesthetic of an Earth animal to an alien species. turians were from the start intended to be vaguely birdlike, and I implore you to check out the early design sketches from one of the artbooks- that crest on Garrus's head was not only at one point more feathery, it was also conceptualized as articulating like a cockatoo's. we were likely robbed of this by xbox 360 limitations. and then we didn't see it in andromeda because turians in andromeda were fucked up enough. krogan are very obviously big dinosaur guys, but their faces also always made me think frogs. salarians are nonspecific amphibians. drell? lizards. hanar? literally just a jellyfish. rachni are crustaceans by way of bugs. even minor guys like the elcor are very elephantine, and the volus, who have never been depicted outside an environmental suit, have those droopy bulldog jowls on the suits. the collectors showing up in me2? creepy bug guys. and I mean, the reapers are big metal squids.
the second category is Star Trek, because it was 2007, and bioware really fuckign wanted their blue space babes. this one's for the asari and batarians, who are practically within the scope of makeup- asari are just blue humans with a headpiece, and batarians are the classic Forehead Alien but expanded upon a bit vertically because they didn't have to settle for TV budget makeup.
the last is the Fucking Monsters, which is where the vorcha and yahg live. they're kinda just scary-looking freaks! they're the monsters because they're almost universally antagonistic, so it's fine for them to just be Pumpkinhead-tier schlock movie monsters.
this is why the angara and kett suck so bad- because they don't fit the vibes, and not in a "this is a different galaxy where everything is different" kind of way. they're just a collection of generically alien traits- weird legs, silly hands, lumps, bone armor, different eyes- with weirdly human faces. they feel unfinished because they don't have that touch of the recognizable that the other aliens do, and it doesn't come across as fitting the story, they just feel like they're from a different game. they have no animalistic features, they're too inhuman, and they're too soft to be monstrous: most kett just kinda look like kenny rogers, and their leader has big baby eyes. take the weird angara lumpy neck-thing and turn it into a cobra frill, and take the kett's faces and give them crab mouthparts and eyestalks, and hey! these guys suddenly feel like they belong!
this is also why it sucks so fucking bad that they built up a Tali Face Reveal and she's just a white girl