I never finished the third one. I kinda want to revisit and finish the trilogy sometime. I remember enjoying the RPG elements but looking back on it, it really glorifies the military, you're basically the space CIA if I remember right. You also team up with Garrus, who's a vigilante cop and the Space Fascist in the third one, whose genocidal racism is treated like "haha he's like your racist grampa lol".
I don't know if it's intentional that the only non-shitty faction is the Geth. But I always found that deeply hilarious considering the central theme of the series.
Quarians are basically Israel in space.
Turians are fascist and also forced the Volus into living under their protection.
Asari are hoarding Prothean tech for the benefit of its religious caste and also keeping slaves.
Salarians are a whole species of CIA agents, fighting proxy wars using other species and then genociding them when they're done.
Krogans just kill everything.
Batarians are open about their slavery and racism against other species, which the council uses as an excuse to treat them like shit even when they do the same stuff but with a veneer of respectability.
I can't remember much about the Vorcha other than them doing all the grunt work in pirate gangs.
Protheans are like the amalgamation of all the other groups worst traits.
What few leviathans are left, just sit back and watch the reaping every cycle.
Hanar keep the Drell as slaves just because they helped them out one time.
But the Geth just sort of chill on their homeworld and it's the Quarians that always start shit with them. Also they help all the races that treat them like shit during the war against the reapers even though they didn't need to pick a side in that fight.
Edit: the entire human race is basically modern day America just with better tech. And a fuck tonne of the military was in bed with Cerberus.