only just got into the amiga emulation thing, so not completed any amiga games for a long time. but from my memory;
remember playing 'wrath of the demon' for the whole weekend wiith my big brother which we completed from start to finish. i borrowed the game from a friend, don't think i played it again after this. that was real fun and a real sense of 'team work' but my big bro will say he did all the work.
monkey island 1. played this for some months/years, but never got to the end. after a sleep over at my friends house, we decided to ultimately try to put it to rest. we managed to get to monkey island for the first time. then i took the save game disk home and completed it myself the next day.
another world took a few months i think.
flashback i think took a good few months also
giana sisters i nearly did but mine always crashed at about level 26.
shadow of the best 2 on the other hand was only ever possible with the cheat.
loads more probably but it was about 10 years ago