What makes it unique is that it is entirely open world - there is no main story and you're free to play however you want. It's almost like a Pokemon version of Skyrim. You can choose to start your adventure in either Pallet or New Bark Town. But from there, where you go is up to you. HM traps, plot-based roadblocks, and other obstructions have all been removed, leaving the whole map open for you to explore from the start. There's even a bridge added so you can travel straight from Johto to Kanto (or vice-versa).  RTC on this cartridge is static. However, each time you start the game you are able to set the clock to change the time. 

 

There is minor trainer customization (appearance and starting town) and you can tackle all 16 gyms in any order. Gym leaders' levels and team compositions will scale up based on the number of badges you have. After you've conquered them all, you can re-battle them at whatever 'badge scale' you wish, to take on their strongest or weakest teams. You need a total of 8 badges (any 8) to challenge the Elite Four.

 

All 251 Pokemon made obtainable

7 different male and female trainer sprites to choose from, with basic color customization

28 different selectable starter Pokemon

Restoration of Kanto dungeons (Safari Zone, Cerulean Cave, Seafoam Islands, etc.)

Following-Pokemon, and unique menu sprites for each Pokemon species

Running shoes, and fast-travel options

Dedicated NPC for trade-back evolution