I've not yet played MM1 or MM2, but I rate MM3 as one of the best-designed RPGs of all time. MM1-5 are turn-based games and the game engines are antique in today's terms, but in terms of the plot and the puzzles, MM3 is superb. There is a lot of dungeon bash in it, but there are quite a few good riddles, and you really do need to think outside the box in order to work out some of the passwords. And if you work out how to use the 4 chairs in the Tomb of Terror properly without looking it up, you deserve a medal

TTBOMK they are available from GOG, although I don't know in what format. If it's DOS, MM3 and World of Xeen (MM4/MM5) run very well (although not perfectly) under Dosbox. Unless you search the web for the answers, those three ought to keep you busy for some time.