The game looks and sounds fantastic because the world is rendered instead of it as sprite-based, you will get shifting camera angles for dramatic effect on some dungeons or just to reveal overall areas better. Most of the game is in 2D while the battle scene and some story scenes are in full 3D. I must say, if you are playing it with the new 3DS, the 3D feature of the game is more enjoyable than ever. However, the previous 3D problems that existed in the previous X and Y still exist here. So, it is a little bit disappointing.
There are quite a few changes in the game, as far as features is concern especially now that Pokemon Omega Ruby 3DS rom is released and available for download internationally. But there are two I would like to mention in particular. The first one is the new soar function. As you progress into the game, you will be able to unlock a Poke flute that summon Latios and will allow you to fly quickly to any town. But the difference here is that you will be doing this in a 3D environment and you will be able to land to specific area of choice rather than the previous HM fly that will teleport you directly to a Pokemon Center. Another new feature in the game is the Dex Nav. You can see in the bottom screen. This nav will provide you 3 awesome things: first is, it will show you any potential special Pokemon within the area rather than just relying on random encounters; the second one is sneaking on Pokemons, the more you successful you do it, the more special the Pokemon can be; lastly, Dex Nav tracks all Pokemons on a given area, caught or not.
Honestly, playing Pokemon Alpha Sapphire on 3DS was a great experience. I was never bored once, never frustrated, and never ever without something interesting to do. Pokemon Omega Ruby and Alpha Sapphire is without question the most fun, and the most refined Pokemon game yet.