His record from 2001-2012 was insane, and was easily enough for him to be considered as one of the greatest managers ever. I did think that his gradually declined as a manager (though his standard for nearly 12 years before that was ridiculous) from his third and finals season at Real onwards, though since then still won trophies during his second spell at Chelsea, Man Utd and Roma.
I've said a few times before, that is work at Leiria with barely a cent to spend, leading them to their highest ever league finish at the time in 2001, and then 3rd place midway through 2001/2002 (ahead of Porto who came calling for him plus Benfica), shouldn't be overlooked. And even before we get to Porto's Champions League winning campaign, clearly their 2002/2003 season with 3 trophies including a UEFA Cup win, was stellar. Porto's value of player sales during Mourinho's time in charge, exceeded their value of purchase players (I'm not using the word profit as a I assumed that a decent chunk of transfer fees on player sales went to third parties). And at the time of the 2003 UEFA Cup final, his Porto team was built on half the budget compared to Martin O'Neil's Celtic team.
The fact that most Roma fans seem to adore him, and the Stadio Olimpico was routinely sold out (which very rarely happened before he took charge) was notable.
Clearly over the last few years though, it has become less and less worth putting up with all the controversy that comes with him. And as other people have said, his management man skills have decline, and he hasn't been able (or willing) to adapt to the extend that Fergie and Ancelotti did.