I'm going to start right out with it. BUY THIS GAME! This game is amazing on many fronts which is why it deserves a buy if you have a DS (maybe even buy a DS to play this game).
The gameplay is as fresh as ever. The formula that GameFreak put down so many years ago still works. If you have already played any of the previous Pokemon games, there are basically no changes, other than the fact of the addition of a few mini games and a pokemon can walk behind you. For newcomers, here's how the Pokemon formula works: You start an adventure with a starter pokemon, and then train to become the best pokemon trainer in the world. You do this by defeating other trainers who roam the land while also catching some extra pokemon of your own. The formula is straight up addictive and the plot is also well done.
It's pokemon on the DS. The game uses the same graphics engine as Diamond, Pearl and Platinum and yes, the graphics aren't top notch. I have definitely seen better on the DS (Mario Kart being a great example), but once again, the entire point of Pokemon is the gameplay and the replay value, not the graphics. As a plus however, many trainers have new animations and some gyms just look really, REALLY good. The atmosphere outside of special events could've used some work though.
I will admit it, I am getting a bit disappointed with GameFreak recycling their 8-bit recorded cries for the Pokemon on every single game. These cries are the same we had 10 years ago. On the other hand, the overall soundtrack is really good, and I have also heard there is a way to get the original soundtrack back in the game by achieving a certain item. In general, the sound is ok, but I think GameFreak needs to do a little overhaul with the Pokemon cries.
Replay Value: 15/10
ARE YOU KIDDING ME? 16 BADGES! 3 TOTAL STARTERS YOU CAN GET! Straight up epic. I, in my own right, already thought that all the other games that only had 8 badges and one region were long enough, but WOW. This game is amazing (I already had the Japanese version, and have played to the second Elite Four, and it's taken me a good 40 hours already) in this criteria for sure.
If you have a DS, BUY THIS GAME. If you don't, BUY A DS, and then BUY THIS GAME. Amazing characters, amazing battles, amazing starter pokemon (who doesn't love them a nice Typhlosion?), and great replay value. You won't be disappointed.