It's like... a Swiss army knife of household appliances. Wanna cut the lawn? Use Rotom in it's lawnmower form! Wanna make some toast? Use Rotoms toaster form! Want to wash your clothes? Hey Rotom~~
Also the addition of a bunch of Pokémon into the Sinnoh dex makes me happy!! Means I get the choice of training something different from the regular Pokémon available. If this means you can get them before the Elite 4 and such anyway.
Hell knows I wanna go through the game training a Houndour as my fire type, that would rock so damn much |D
I'm really looking forward to Platinum so damn much X3