I agree, the coup is pretty much a win for Shepard. The victory might be bittersweet, but Shepard still foils Cerberus' plans there.
No he/she didn't. Kai Leng was what caused the mission to fail. He's labeled as an assassin, then make him an assassin. As soon as he lands behind the councilor, he kills her and runs to the skycar before Shepard jumps out the window. Kai Leng encounters Ashley/Kaidan, kills them very easily and does whatever with the councilors.
This is what we got
Kai Leng stands in front of the councilor hesitating to kill her.
Thane shows up with a pistol at Lengs head. Shoot the guy Thane..
Thane and Leng fight. Leng is thrown to the ground
Why isn't Shepard and squadmates not firing at the guy?
Thane decides it would be better to play chicken instead a shooting at the guy from where he was standing?
Sword. Say hello to Thane. Thane. Say hello to the sword
Leng runs away
The best part is when Commander Shepard asks "how bad is it?" At that moment, Thane could've redeemed himself by shooting Shepard in the gut and say "you tell me"
With Kirrahe, the guy is in cloak mode. Shoot the guy
Instead he gets shot and dies. Had he shot Leng while in cloak mode, he might of lived.
How hard is it to turn the sky car sharply causing Leng to fall off the skycar? I guess that sounds too easy. Or why didn't Shepard shoot Leng after he stabbed the car and dropped his bubble?
How about throwing a grenade in the elevator? If you don't have one, have one of the squadmates throw one if possible
When facing Ashley/Kaidan, why aren't the squadmates speaking up on Shepards behalf when Udina says Shepard is working with Cerberus? Ashley/Kaidan should also realize that they don't have a chance. They might injure one of them, but would be shot very quickly. Both should also realize, if Shepard is working with Cerberus, they wouldn't be talking at all. Remember Mars? Cerberus didn't waste time talking, they just shot at everything that moved.