I cannot really say 100% if this game was worth it or not. I've played all the other Monkey Islands in the past, and besides Monkey Island 4, I enjoyed all of them.
I will review this game from different points of view:
1) CHARACTERS: Guybrush never gets boring, he is still able to make you laugh and give some funny commentaries on what is happening to him even if the situation seems hopeless. His wife Elaine is even more annoying than she ever was, and also this time she's one of the main causes of Guybrush's trouble. Le Chuck is seen for the first time as a human, and the Vodoo Lady has some nice corpse paint on her face. Even some old acquaintances have found their place in the game. There are a couple of good characters which worked well, like De Singe and Morgan, and the side characters also were well thought and hilarious (like the sailors belonging to De Cava's troupe). All characters were well thought and well designed.
2)STORY: The story is "innovative" and well thought, and has some nice little twists in it which keep you interested. The fact that it develops over 5 episodes, though, makes it sometimes "slow paced", but overall the whole idea works very well, and keeps you wanting to know what happens next.
3)GAMEPLAY: that's the main point which ruined the whole experience for me. Until the 4th episode I was able to manage everything by myself, without getting any "help" on the internet. Starting with the fourth episode, I had some troubles understanding the map the Voodoo Lady gives you to make the Esponja grow, and after some failed attempts I had to look it up to continue. The game also had a bug I could only solve thanks to a German blog, and some of the stuff I found in the fourth episode was pointless (the liquid glass, the wax, etc.), and made me loose a lot of time trying to find out how to use it. In episode 5 I got REALLY frustrated and had to look up for a solution too many times. I can say I am an experienced point&click adventurer and always manage to solve everything by myself, but this time the connections between objects and effect was "absurd" at times, so that I would never ever have thought about the combinations that were needed to go on. The whole going back and forth through the Crossroads was kind of an annoying time loss I would have avoided, and the "advises" the Voodoo Ladies gives you are not really helpful in finding out what to do next.
So, overall, the game was well done (even if there were some mistakes in the German synchronisation, and sometimes you could even hear the same guy giving voices to two different characters, which is never good), the story was nice and worked very well, but the Gameplay ruined my overall experience, so that I just wanted the game to finally be over in the last chapter.