Pokemon Flora Sky is my personal favorite ROM hack based on the Emerald version. Remember that you will need a GBA or DS Emulator to run them. So, here are the best Pokemon GBA & NDS ROM hacks that you must play this year. Some of them also offer new Pokemons (called Fakemons).
You can find all the Pokemons in the wild, new palettes, new regions, new music, and a complete overhaul of the story. It is just like playing a whole different Pokemon game. There are countless new things you can get with them. The Pokemon ROM hacks are a solution to all of this.
There are limited Pokemon availability, complex evolutionary mechanisms, and a bland storyline.
However, the original game versions come with a lot of restrictions, limited features, and very little freedom.