I didnt like gen 5 trailers when they came out, didnt buy it but after a lot of years i decided to give it a chance and i love it, then got my O3DS and played all the games for it (Oras, XY, now Monn/Ultra Sun) and i can tell you, they are all Pokemon. Is the same. If you like Pokemon, you would like this game.
Times change, forget nostalgia. If you want that, play Platinum again (I always start a new Platinum save, my favorite game). Next gen would be even more graphical, thats the way things go, but the game is the same and is fun.
US/UM has a lot of content, way more than S/M, give it a try (if you have the money, of course) and as a good gbatemp user, i would recommend to install a CFW so you dont have to pay for it and get it when you want.