The original Zelda holds up surprisingly well if you use a guide to locate the dungeons. Going for 100% in the main quest was pretty fun and it felt rewarding going from being so vulnerable to being able to dish out a lot of damage.

2nd quest on the other hand does not hold up. Lot's of enemy spam in dungeons (especially the darknuts). None of the other changes stand out to me enough to make playing through second quest worth it.