Ichigo's power ups dependent in his determination and protagonist power, instead of his pedigree. Each time he stumps against a wall of centuries of experience, abilities and power, he trumps it because he's still human and his soul is in developtment, each time that he should be snuffed he gets again and again demanding more from his power and his soul giving him more.
That battles were decided by cunning and ability instead of who has the biggest stick, that Aizen could LOL NO your powers not because he was ubber powerfull, instead had him planning for centuries for each way their enemies could kill him, no bullshit immunity to Zanpakuto powers or spells, that kind of thing only works in plot armor for Ywach, Ichigo and maybe Yamamoto, not for every villain, being stabbed even for a weak Shinigami should be dangerous, have battles of rock-paper-scissors of the Nasuverse variety, not battles of measuring power levels.
Hollows actually becoming dangerous not jobbers, a HOLLOW SOULD'VE infinite potential, even more a Vasto Lorde who is an amalgam of billions of souls (kind like akumas level 4 in D. Gray-man) even a captain shouldn't just stomp hollows, at this point Soul Society are just bullies instead of an outnumbered army who can varely survive protecting the human souls.
Kill characters, make me bleed with each death, make them tragic, painful to watch make the characters matter instead of walking fanservice, make the villains menacing, anyone can die, obviously not anyone but make me believe.
Give humans characters more important parts, don't sugar coat the Shinigamis are assholes (except a core group associated with Ichigo) and Soul Society is a terrible place to be.
And last Make Ichigo the hearth, the soul, the determination of a rag tag team, make him charismtic enough to have Quincies, humans, shinigamis and hollow being one percent loyal to him, give him ideals beyond protect his friends, make him Shinigami/hollow/Quincy Jesus