No it really isn't. Just the last boss, and the latter magma hideout levels. So just stay away from late magma hideout and do it early instead and you got yourself an easy game.
And chefcook-9000 can also be hard. And the black dessert desert too. Sir sweets castle, Darth Moab, Sweet Garden, all last day levels too.
Martial tower and the downloadable stages are hell though.