It's a little weird (the level of criticism). In his 5th season, monster production. Could he be better? Yes. So could everyone in the NBA.
As for his finals performance:
27 ppg
6.6 Apg
6.4 RPG
2.2 TO pg
.433 from the field
.824 from the line
He was easily the 3rd best player in a finals that included Lebron, Wade, Bosh, Durant, Harden, Ibaka. He gets criticized for shooting in the finals, but with Harden dropping a stink bomb and two of the best wing defenders in the NBA blanketing Durant, Westbrook was the bailout option on every single offensive possession.
Now, it is an interesting question (as I posted in another thread) whether OKC should have traded Westbrook or Harden based on what they could get in return. But both are franchise cornerstones. Just because they are not as good as Durant doesn't mean they shouldn't stay on Durant's team.