Namco-Bandai sure made their money's worth with this. It's fun, but can get repetitive with leveling enough to be top.
Upon playing Digimon World DS, I was surprised at how fun it actually was. It may feel like a Pokemon game, but some things are different.
The first obvious difference is the way battles are fought. Random encounters are prevalent, with some key battles. The battle screen however, looks like a mod off of earlier Dragon Warrior/Quest games (showing your opponents, but not your team). Another great thing is that you're shown the battle order, so you can plan your battles ahead of time to minimize how much damage your Digimon take.
The next difference you'll notice is how you can raise your Digimon on farms (like the Day Care in the Pokemon games). What's cool about this feature is that you can directly affect how your Digimon develop, and there are a certain number of quests they'll ask of you throughout the game.
Probably the biggest and most important difference is how your Digimon level up and evolve. They level up regularly with every battle, but you can choose when they evolve, and sometimes, what they evolve into. You may have to do a few things to reach the evolution chain you want, but in most cases, it's worth the wait.
If you're tired of Pokemon games, this game might not be for you, but if you want to see what the differences are, go ahead and try this game out.