He cried, angry raged and killed demon's without any particular goal, had to be calmed down by Dante before he got himself killed by being reckless, and then he TRIED to do something about the situation but got captured by the enemy immediately.
1) Yes, he did cry an raged. But what does "killing demons without any particular goal" has to do with anything? He killed them because
they were in his way. Not because he had no reason to.
2) He was initially angry at Dante because he was about to cause harm to Kyrie in the beginning, as well as killing Sanctus before that. His mission was to follow Dante and kill him. That is why he was angry at him in the beginning.
3) He didn't get "reckless". He was about to finish the job until Sanctus pulled a classic move by bringing Kyrie in the fight, which then cause Nero to
hesitate and get caught.
actually he spends about a mission or two just whining about it without any particular goal he just kinda killed demons in a rage.
I don't remember him whining for no particular reason
during his missions about Kyrie. The only times I see him talking about her is when he talks to Credo, Agnus, and Sanctus. If so, you're gonna have to provide examples.
He then left Dante to pick up all he pieces since he didn't actually destroy any of the portals and only killed one of the bosses and it was a underling. The entire first half is Nero being a uninteresting and later on a angst y devil hunter and the second half is just Dante cleaning up his mess and doing everything Nero should have done on his first run through the campaign.
I'm pretty sure he didn't destroy the hellgates because that wasn't his main objective. It's still sloppy on his part though.
As for you not thinking he's an uninteresting character, it just sounds like you personally don't like him, which is fine. But not liking him is completely different than describing his personality and motives incorrectly.
It's alright if you didn't like him, no one will think any less of you because of that. But it sounds as if you are only complaining about his "angst" when is quite obvious he is going through major stress having his girlfriend taken from him by people he trusted as well as being hunted down/almost killed multiple times.
It's not like he's strolling through Fortuna complaining about nothing. He has legit reasons for being upset. If someone you trusted/looked up to suddenly used you and took the one person in your life that meant something to you, you'd be upset yourself.