Most of the bosses are extremely easy hands down once you memorize their patterns.

Actually(sort of on the subject still), that's one of the major problems with single player on JJ2. The enemies are so patternistic and follow a set animation path. This allows people to memorize what they do easier and once the memorization is mastered, they can slaughter the game.

Now, if the level is something like QoB, THEN it is tough.