Not nearly as fun as the original, but good enough for a sequel.
The game starts out good, fun and easy to beginners. But once you get around world 4, the game gets harder than Yoshi's Island's max difficulty, which was probably the final fight. The game gets so incredibly hard, you'll probably need close to 50 lives to complete one level, and that will get irritating to most people. But of course, there are hardcore gamers which will find going through the majority of the game quite a breeze. To most though, it'll still be fun, but too hard to keep you playing for a while.
Now, there's more than one baby to choose from. You can switch them at stork stops spread throughout the level. But most of the time, you'll be sticking with Mario. He is the best for new players, while everyone else (besides Peach) is kind of an increase of difficulty by sticking with them. Baby Donkey Kong, Wario and Bowser, aren't much of help overall. All Donkey Kong does is slow you down and gives you the ability to climb vines, which is only helpful in a few stages. Wario is practically a nuisance. Rarely used, he attracts metal objects to his magnet, which doesn't work too well. And you would think Baby Bowser would be fun to use. You would be wrong. He slows you down like DK and Wario, and disables your tougne, which is a problem for small enemies. You can still get eggs and throw them, though.
The music is kinda pleasant to the ears. To some, a little too pleasent. It's more easygoing than the original, although it's not to get overexcited about. The sound effects, well, it depends on which ones your talking about. Yoshi sounds as cute and funny as ever, although there is actually no new vocals for him. The SFX of the enemies sound alright. Some are kinda weird, but most are alright and shouldn't be a problem either. But the babies, just seem 3 times more annoying than in Yoshi's Island. Baby Mario's cry is really short and blunt, and repeats fast, so you'll want him to shut up most of the time. Try to not be in the harder levels with him, or you're ears will bleed. Baby Peach's is the most realistic, but it's kinda loud and annoying. You'll get used to her's though. Baby Donkey Kong, I don't even know what to say. I can't tell if he's crying or laughing once he's flys off of you. It's that weird. Wario is just, VERY FREAKING ANNOYING. THE LOUDEST AND ANNOYING OF THEM ALL, not even sounding original. Bowser's is probably the only good one. He actually has the voice he has had in the previous games, so his cry is actually not bad. The graphics, meh, they're good for a 2D platformer, but it could be better considering it's a DS game.
So, to me, this game is too short and a little too hard to actually stand out as one of the good Mario, or DS, games. Any hardcore Mario or Yoshi fan should go ahead and get it, but anyone new to this kind of genre or game should just rent it. Most people like it though, so it's your choice. And this review is my opinion, not yours.