The same concept, a new world. Your travel will begin... again.
First of all, I just want to say that I really enjoyed the game. It gives you the old Pokemon feeling of "gotta catch them all" and battle with your caught pokemon. Either against trainers or Gym Leaders.
If you want some big improvements, the game is for you. Thanks to the Wi-Fi system, Pokemon Trainers may battle against each other, playing with each other and rivalizing each other (a lot of "each other" there). Except from the Wi-Fi and of course new pokemons, there is no bigger improvements of worth (according to me). It´s like any Pokemon game out there with a cool network improvement if you are to sum it up. It´s still isn´t the ultimate pokemon game everyone is looking for, but it´s really close thanks to the more realistic feeling.
For the gaming in general, I miss the Fire and Blue versions actually. They felt so epic and well-thought. This game misses the heart of the creator like Red and Blue had. It´s still a really good game, but you will feel there is something there missing.
The joy of catching pokemons also got bigger. Thanks to the more advanced Pokedex (the collector data for catched pokemon) is a really nice improvement. Sadly though, I don´t think too many gamers would care about it enough.
A new world is waiting for you. It may not be fantastic, but it will be a magical journey which you may want to return to a lot of times.