Keane was an unbelievable and unquestionably world class player (Fergie clearly deliberately excluded him from his list of world class players through pettiness). He had a tremendous passing range to go with his other more vaunted attributes.
And on top of that, I think he is a garbage pundit. He has some entertaining soundbites, but I think he overplays the whole a'ngry man who hates everything' routine. Plus his actual punditry largely consists of buzzwords like 'character', 'leadership', 'desire' etc.
And the way he holds on to grudges is pathetic. Remember when he raged at Carrick merely getting the Man Utd managerial job on a caretaker basis for 3 games in 21/22? And him still being bitter towards Fergie after all this time, including after Fergie had that life threatening brain haemorrhage 8 years ago, reflects very badly on him.
The fact that Man Utd had that golden period from 2006-2009 after he left, and that Carrick (who took his shirt number) came in and did better than many people expected, clearly enraged Keane even more.