all games are not created equal

The inclusion of voice acting and some very well done hand-drawn character sprites really made The Curse of Monkey Island (or Monkey Island 3 if you prefer) really make you feel like you're playing a cartoon.

Both games really do great with modern-day humor and 4th wall slapstick.  For example, in CMI, Guybrush fakes his own death, to which a nearby patron says "Strange, I didn't know you could die in these Lucas Arts adventure games".

SMI was instantly a classic and still holds strong in terms of adventure games of old, and it was so clever with it's humor that it stands strong today.  However CMI's similar humor with excellent voice-acting just makes every joke that much funnier.  Insult-sword fighting in SMI was great, but in CMI you get voice acting PLUS the insults have to rhyme.  It's great.

One thing to note is that there's many puzzles in CMI where the solutions don't make since until you just randomnly stumble across it through random clicking.  Then when you finally DO get the solution, you can't help but think "How the heck was I supposed to figure THAT out?"
SMI doesn't have these issues quite as much.

CMI is just incredibly witty and all the characters are just loveable.  Whether it be the barber pirates who'd rather sing than man a ship, or a demonic talking skull, the game is just a joy from beginning to end.