The Legend of Zelda: Outlands for the NES is a proper sequel that continues the style of gameplay that made the original Zelda so popular. It’s an unofficial fan-made sequel, but from everything I’ve been able to read about it, it’s absolutely true to the spirit of the series and is a really high-quality ROM hack.
It turns out the author of Outlands has been hard at work on a sequel to the SNES Zelda as well. Zelda 3 Challenge: Quest for Calatia has been in development for the past three years. It’s still a long way from completion, but it’s fun to see people making brand new games out of dated but much-loved game engines.