Something I've heard some reviews bashing on and that's Star-Lord losing it over 'aw he killed mah girlfriend' and going nuts on Thanos. They need to consider the past few movies and just what Star-Lord's been through. When he was a kid, his mother died and he was abducted - no connection to anyone, completely alone as a literal stranger in a strange land. Learned to fend for himself, and only himself. Always wondered who his father was - finally MEETS his father. Finds out his father murdered his mother. Kills off his own father - and loses his daddy in the process. All this time he's had nothing but one-night stands at most with people, remember "oh wow I forgot you were here" at all?
Now he's finally, after years, made progress with Gamora, and he's opened up to someone - and just like before, this hyper-powered jackwagon with delusions of godhood and knowing what's best for all life in the universe? Kills her.
I don't blame him, and I'd have loaned him ammo for going after Thanos at that point. Everything he'd lost, all at once, in GotG2, and then eventually opened up again, only to have it cut off before it can go further? He's not a well-developed, thoughtful, slow-burn kinda guy. He's wearing his heart on his sleeve and Thanos just stabbed it.
