Windu has his good points and his bad points. It's just that some of them are the same points.
In terms of combat ability, he can't be matched. Sidious vs RubberBouncingBall!Yoda did not go terribly well for Yoda, whilst Windu managed to take down SIdious effectively solo. (I mean, he had backup but they died so quickly they don't really count.)
Other pluses. Dude is resolute and incorruptible. Windu is not the type to fall to the Dark Side, no matter the circumstances.
He's deep into Jedi Orthodoxy, and for him that's worked very well.
But what looks like incorruptible resolve from one angle looks like zealotry from another angle.
At his best he's a bastion of the Order, at his worst he can't understand why everyone can't just do it all right, like he can.