I took an hour or so and made up this flowchart of the puzzles in Monkey Island. Yes, I did this for fun. I guess you could call it a walk-thru. What's interesting is you can take any point in the game and crawl up the chart to see what all MUST be done to get to that point.
Far as I can tell, there are three "alternate solutions" to puzzles in Monkey Island. I've noted those on the image. See if you can recall them before you look at the solution. Further notes below.
The 11 dark-colored boxes are puzzles that are more creative than the standard inventory and dialogue puzzles. Adventure game designers today would be well-served to make more puzzles like these! SMI is a very simple game, but these types of puzzles really make it memorable:
1. Sneaking into the kitchen (simple but good and very tense the first time)
2. Taking the fish from the bird
3. Following the storekeeper to the Swordmaster's house
4. The nature of the Melee Island treasure "map"
5. The whole insult swordfighting sequence
6. Stealing the note of credit from the storekeeper
7. Freeing Otis from jail
8. Negotiating with Stan (technically just a dialogue puzzle but very unique)
9. The artwork catapult
10. The monkey totem pole assistant
11. The navigator head guide
You could break the game into 5 parts by separating the ghost ship from part III, which is completely within itself. You could almost break it into 6 parts (split up Part I into before and after you finish the trials) except that the chicken and Meathook's house could be accessed before or after the trials. Everything else is split up on either side of the trials.
As the game goes along, it gets increasingly linear, which gives the feel that events are moving much faster. In the game's first half, you do many actions without accomplishing much; in the second half, every action seems to drive the plot along.
I was surprised how much "smaller" Part III is than Part I (27 boxes to 39 boxes). Time on Monkey Island always seemed longer to me, but I suppose it's because the map is so large. But there are probably less rooms.
As I said above, SMI is a very simple game compared to MI2 and CMI, and compared to most adventure games today. But I think what made it stand out was the characters. Characters rarely seemed like puzzles to be solved in MI1, whereas in TMI I immediately got that sense. In SMI, there are many characters (Meathook, Men of Low Moral Fiber, pirates in bar, Smirk, Toothrot, voodoo lady) whose characterizations far outweigh their in-game utility. Characters always felt like people, not objects.
As I aspire to design adventure games myself, this little project changed my perspective some. Before, I thought the design of an adventure game should revolve around great puzzles, like DOTT. But SMI is really based around characters and atmosphere first and foremost. Some smart puzzles are necessary but they don't have to be hard or complex. In fact, puzzles that are too hard can get in the way. Good characters and setting can take you a long way.
This project also reminded me how EASY SMI is compared to MI2. It takes time but is a very easy game by LucasArts standards, perhaps 3rd easiest after Loom and Maniac Mansion. Once again, the game doesn't have to be hard to be good. Let characters and setting and dialogue do all the heavy lifting, then insert puzzles that are interesting and not annoying. It's what made SMI the greatest adventure game of all time.
p.s. I'm thinking of doing MI2 as well but it will be a LOT messier. I don't think it'd be possible to chart it without a lot of lines crossing. The bulk of the game is very non-linear but also very inter-dependent.