You can't hate this game by any means. And why should you try to?
The game itself is rather short.
Boss battles are way too easy.
There's no story.
Music isn't strong enough for my tastes.
Now what's good about this game, then? Everything else.
Mario keeps his jumping arsenal from Super Mario 64, level designs are way above the level of any (mario-)game I've ever seen, and those two combined make for some highly concentrated fun. Highly concentrated, yes. You can complete this game in under two hours, but then there's still all the secret passages to uncover, and believe me: there are a LOT of secret passages. But that's what you've come to expect of Mario. When you're done, there's still a large array of minigames to play. I spent over 10 hours only whacking Monty-Moles myself, so let me tell you: these minigames don't get old in one day. Or one week. Or one month. And apart from bragging about highscores in front of you friends, ypu can even play most of these minigames with up to 4 players. There are even some multiplayer-exclusive games.
There's no story. It's not like anyone cares though. Next one.
Music. The music in a Mario game will never score a 10, but 8 points is fair because the music is catchy as always, like it should be in a good Mario game. Nice extra is the oldskool level completion tune you hear when finishing a level with the last two numbers of the amount of time there's left being the same.
Boss battles are way too easy. True, and this is a in fact a major flaw of the game. There's no frustration in this game, Mario does everything you want him to do, and you can easily count the number of lives lost in your first playthrough. In a way, the game's too easy, which certainly adds to the fun, but "bosses" can be taken out from a distance if you have the fire flower. On a number of occasions, you'll feel relieved when you see the door to a boss battle, because you know it's gonna be easy and you're saved from those tricky goombas and koopas. Completing Super Mario Bros. 3 for instance, felt much better because it was in fact pretty hard to do. It's the only major flaw of this game.
One last thing to discuss are the new power-ups: a mini mushroom, a big mushroom, and a koopa shell. The mini mushrooms turns you mini, allowing you to enter tiny pipes, walk over water and jump higher. This power-up's pretty cool. Then there's the big mushroom, which turns Mario (or later on Luigi) into a giant, destroying all that's on his path. In level one this power-up is awesome (you can even destroy the flag at the end of the level), however later one, levels aren't designed for use of this mushroom, and you're better off not using them anymore. Which is sad. Finally there's the koopa shell that basically turns you into sonic, with the main difference being your ability to bump a wall and sliding in the opposite direction. It also allows you to swim faster, which comes in handy pretty often, and you can shield Mario from all harm simply by crouching. Probably my favourite power-up in this game.
In the end, this game is pretty much solid. But that's not enough for a "superb" score: it offers nothing really new, it's basically Super Mario Bros. 3 fused with Super Mario 64, plus the Super Mario 64 DS minigames. Still, I strongly recommend buying this game to anyone who loved the 2D Mario platformers. And I'm pretty sure that's every gamer out there.