There are several rewards for repeatedly going through the relatively unchallenging battles in this game. You'll be able to download a special version of Pikachu to your Diamond/Pearl cartridge after you beat the game for the first time. This Pikachu knows two moves that it can't learn under normal circumstances (Surf and Volt Tackle) and holds the excellent Light Ball accessory.
As you progress, you'll also earn new backgrounds for your trainer IDs and currency called Poke Coupons. These can be used be used to buy new clothing for your avatar and to purchase additional items that can be downloaded to the DS game. This is another case of the game being far more appealing to hardcore Diamond/Pearl players. Buying new clothes isn't a big deal at all, but purchasing additional attacks, berries, evolution items, and more can be very useful to ardent Diamond/Pearl gamers.
The only aspect of this game that can be considered revolutionary is its online play. Similar to Diamond/Pearl, this is the first game in the Stadium/Colosseum series that can be played online. You can battle random players with all your Pokemon set to level 50 or challenge your friends (through Nintendo's dreadful Friend Code system) with a slightly wider set of rules. This is, by far, the most fun we had in the game. While so much of it depends on who you play, the 30+ battles we played online were much more challenging and enjoyable than competing against the dopey AI in the offline game. Having said all that, we would have liked to have seen more options in online play - rankings, matching up skill levels, voice chat, etc. are fairly common online offerings found in other games.