His work finishing WoT is better than a lot of his own work. I think he's publicly said he wouldn't finish ASOIAF though. I'm sure part of it is out of respect for the GRRM who is still alive, but also Sanderson isn't really capable of writing adult themes and situations due to his mormon background, so he literally wouldn't be able to adequately complete it.

>We did this already and everyone hated it!

Because they rushed it in a way that made no logical sense.