I think Tomoya is a character with a huge amount of depth. You can’t assign a specific character trope to him, nor can you describe him easily. His personality is quite complex and it consists of many layers.
And it really needs to, because Clannad is a story of pretty much his entire life, not just a fraction of it.
Tomoya used to have a fulfilled life in his teens. He had a hobby and he was good at it.
But it all fell apart when he got into a fight with his drunk father and sustained an injury that would leave him with a permanent disability. Both his family life and his school life were destroyed. He quit basketball. He couldn’t forgive his father. Even worse, he couldn’t stand being in the same house as his father, so he just killed time somewhere else all day and only returned home late at night. That, in turn, caused him to sleep in every day. He was constantly late to school and he was too sleepy to concentrate properly during class. So he fell behind and was labeled a delinquent. And he didn’t even care. He even started hating the town he lived in.
Only by interacting with other people, finding new friends and a lover and expanding his social circle did he slowly start to enjoy his life again. Not only that, he also found new strength. It was the strength that he needed in order to overcome future trials, for fate was by no means kind to him.
He isn’t an actual delinquent, but he would give people a nasty glare or even get violent if need be. He’s kind and dependable, but on the other hand, he’s also somewhat of a mean jerk, especially towards Sunohara. And he’s really funny.
I think Tomoya’s biggest fault was his stubbornness about everything concerning his father. He was generally very reluctant to adress his personal problems, but this is an especially heavy case. It took him way too much time and a staged encounter to finally forgive his father and reconcile with him.
Let’s try and remember. Didn’t it seem like Tomoya got punished specifically for still distancing himself from his father when he lost his chance to get promoted due to Naoyuki’s imprisonment? He could’ve easily prevented that.
As far as decisions, go, apart from the already mentioned father problem, I wish he’d prioritized the safety of Nagisa and Ushio more. He should’ve made Nagisa stay at the hospital when she was pregnant instead of ignoring the risks in favor of some additional happiness. Similarly, he should’ve swallowed his pride and accepted Akio’s money and help. I’m not saying that he could’ve avoided tragedy completely, but those decisions did strike me as quite careless.
What I liked most about Tomoya was his… humanness. He’s easily one of the most believable characters I’ve ever seen. He was by no means perfect. In fact, he was full of flaws. Yet he also had the merits to balance it all out.
What I also appreciated was to see his development. He started off as an unsocial delinquent, but he became a hard-working and respected member of society despite everything that’s happened to him.