His pre-1925 stuff has a decent amount of good points. He was a great theorist, Permanent Revolution and Transitional Programs are both approaches with a lot of merit if taken critically and applied only to appropriate circumstances. Even Lenin admitted that he was the most able, whatever his (many) other failings.

His tactical political leadership with his own clique was also good. If it wasn’t he’d have died alone and forgotten.

But he needed someone like Lenin to moderate those ideas into something amenable to the extant conditions, rather than Leeroy Jenkins-ing everything in sight. That along with irritating literally every Old Bolshevik in existence with his terrible social skills and obnoxious personality doomed him, and he only got worse as time went on.

Stalin actually offered him co-leadership. And he refused, thinking he was so obviously correct that the party would follow him. That’s classic Trotsky right there.