Played the DOS version in 2003 after searching for Adventure genre reviews on this site. Upgrades are indeed worth it.
I remember playing this in 2003 at the age of 18 in ScrummVM. I didn't even know about it until I completed Funcom's The Longest Journey and went off searching for Adventure genre reviews. I was solely a console gamer all decade. I became a PC gamer in like 2000 after owning Diablo 2.
The Secret of Monkey Island was a slightly short, but magical & artistically masterful game. Meaning it was not great as a game, but it was an amazing experience.
Monkey Island 2: LeChuck's Revenge is almost exactly the opposite. It is a full scale production that probably still ran over budget even after the success of the first game. It's bigger, better, and I think I already said bigger. But it somehow lacks a certain magic the original game had. Fortunately, it makes up for it in all "game-y" areas.
Monkey Island 2 is a vaguely "open ended" Point & Click Adventure with more puzzles, almost all of which are better. The music may not be as memorable, but it's somehow more fitting, and its pseudo-dynamic nature really bends to the emotion of each individual scene. There's also not many silent places in this game, which makes the whole experience more lively. Speaking of which, this game is funnier. A lot funnier. There's more jokes than you try to shake a stick at; several times.
I didn't plan this very well, but I'll wrap up and make my final statement on the game. Monkey Island 2 is a bit less of an experience than The Secret of Monkey Island was. It is, however, a much better game than the original in every other aspect. I'll leave it up to you to decide which you prefer.
If you have ever played Monkey Island 2 on your Amiga or PC two decades ago, your friends will enjoy it with you in your buddy time despite the 2 decades stench. I rate this above the Final Fantasy remakes.