>>91248437X-Treme wasn't the basis of most of the criticism. It was created for Claremont to do his own thing.
His two returns to the core X-Men books are where a lot of the criticism comes from. His 2000 return was terrible, though it's hard to say how much of it was his fault.
Then he came back to Uncanny X-Men again in 2004 and it wasn't anything special.
He also had a habit of trying to push his pet characters even harder than before, like Sage. This drove people nuts on his Exiles run for example.
Accepting that he's an old-fashioned writer who will never be able to match what he did from 1975-1990 when he had almost complete control of the book, his work isn't the worst.