Pokemon Platinum, like Diamond and Pearl before it will probably stay as DS's top game for a long time, you know how Pokemon does that right? But for those not in the know, Platinum will still be in the same world as the previous two, with just new Pokemons and some plot twists there, so in a sense it will just feel like a downloadable content of some sort. But for Pokemon fans and maybe newcomers this will still be a good play for the long run as this game really has that factor that makes it addictive even if it's just old school turn based RPG; the reason may somehow be connected to the "Gotta Catch 'em Call" slogan of the franchise as the collecting part may be what keeps the fans coming back for more. So more pokemon simply means more to collect and finally, more hours of playtime.
A Game Guide for those new players can be found here: Pokemon Platinum Version Primer Guide.