I played it when I was... I dunno how old. Maybe 10 or 11? I played the first two Monkey Islands as a kid in the early 90s and I was really excited about this sequel.
I remember having fun with it, but I preferred the artstyle and atmosphere of MI 1 and 2. Overall, I enjoyed it.
When I replayed it as an adult, my opinion stayed pretty much the same. It's a very good adventure game, but it doesn't quite reach the excellence of MI2 (but then, no adventure game does). It does some things that are weird and made me scratch my head as a kid, nowadays I understand how hard it must've been to work with MI2's surreal ending and write a sequel that makes sense of it. Actually, the team did an admirable job, considering how confusing and surrealMI 2's ending was.
Not much of a fan of the artstyle, I still prefer the realistic with quirky elements of MI 1 & 2 (especially 2 is FUCKING GORGEOUS), but I do have to admit that it's very detailed and high quality. You could show some of its cutscenes on TV and nobody would notice that it's from a game rather than a cartoon show. Personal taste aside, the artists did a great job there.
The humor is top notch. Guybrush is more similar to how he was in the first game, not only in looks but also personality - he's more naive and less sarcastic than in the second game, but the dialogues are funny throughout. There are references to the previous games, there are recurring characters, there are new characters which are fun (like Murray, or the pirate barbers), and most of the jokes are pretty good.
Puzzles are good, too. The typical weird logic of the previous games made it into this one, too.
Also, you can't talk about CoMI without mentioning this:
I didn't actually see this cutscene when I was a kid because I had the German version, and instead of translating the song they just cut it.
Overall, it's a very good adventure game and I'd give it 8.5/10 points, with MI2 being a 10/10 and MI1 being a 9/10.