There is definitely a difference between recent Pokémon games such as Pokémon X and Y and the upcoming Ruby and Sapphire remakes, this come in comparison to the original Pokémon games all the way up to about Diamond and Pearl. The noticeable difference has happened in just how much art styles, technology and the power of a console has improved and with each time making the games look even better even just a simple remakes showed a severe improvement in look compared to the original game. This is what it is all about, the image at the top is a comparison showing three sequences in both games and really showing just how much the games have improved.
The first image comes from the start of the game and we already know from our time with Pokémon X and Y that the battle look and design has improved and you can easily see just how improved it has been it eleven years with better detail presented then just a flat and possibly uneventful battle.
The second image is set just outside the Rustboro city gym and again the detail is incredible, I always liked Rustboro city back in the day but the level of detail and the design just makes things look better and again not so flat.
Lastly the third image is the Rustboro city gym and you can definitely see the level of detail added, I mean no offence but the original Rustboro gym was pretty bland as you can see but the new one is really incredible the addition of a museum looks like a natural fit and the skeletons in the back just look really cool, hopefully we see similar improvements in other gyms.