I was recently blown away by Pokemon Emerald Seaglass. It features a complete graphical overhaul in a style I find absolutely stunning, an upgraded Pokedex, includes all Pokemon from Gens 1-3, adds overworld sprites for Pokemon followers, upgrades the battle system (things like inclusion of Fairy type, Phys/Spec split, z-moves), adds some new mini games, and way more.

Find out more on the official site.