A satisfying throwback to the original game, although it suffers a bit from staying too close to the original.
From the beginning level it is obvious that the game caters to fans of the original and several levels are directly inspired by that game, from "Castle of the Big Burt Bros." to "The Cave That Never Ends". While the nostalgia is nice, it is often so prevalent that you sometimes get the feeling that it's trying to be fanservice first and its own game second. Nonetheless, the game does have many of its own creative levels made possible by the baby-switching mechanic. Each baby lends different abilities to Yoshi. For example, Baby Mario allows Yoshi to dash and makes M blocks appear, Baby Peach can float and ride air currents, and Baby DK can swing through vines and make Yoshi's eggs explosive. While it may sound like a gimmick, it is actually nicely integrated throughout the entire game, with many stages taking advantage of all the babies' abilities. A particularly memorable use of this is the final main stage which has branching paths with each individual path taking advantage of each baby's abilities. Another one is an extra stage which is nonlinear and requires you to find 5 number balls and throw them into slots in a certain room to reach the exit, with the paths to each only accessible with a certain baby. The bosses are also very creative and are monumental enough to take advantage of the dual screens.
Yoshi's "health" is determined by Star Points, which decrease as the baby gets knocked off by Yoshi getting hit and floats randomly in a bubble with an annoying cry. When they reach 0, enemies swarm to take the baby away. Of course, gamers merely looking to get through the game generally don't have to worry about the meter as it falls slowly and rises back to 10 after the baby is regained. The real hazards are the plentiful bottomless pits, lava, and spikes which result in an instant life loss when touched or fallen into. Yoshi's flutter jump ability which allows for much aerial control helps in dealing with these, but they are often difficult to navigate. That might turn some gamers off, but others will appreciate the challenge.
The point system from Yoshi's Island returns, with 5 Special Flowers and 20 Red Coins scattered through each level with the requirement of getting all of them while keeping your Star Points at the maximum 30 for 100 points in each level. This adds a depth to the gameplay for completionists as the objects often require skilled platforming ability or clever puzzle solving. In addition, while it is normally very easy to keep your Star Points at a level necessary to survive, it is challenging to maintain a maximum level, although there is an exploit for producing star-releasing eggs that make it easier to deal with. Getting 800 points unlocks an extra stage, so there is significant motivation to get a perfect score.
There are also plenty of extra features in the game. The minigames are for the most part fairly lame and nowhere near as memorable as those from the original. The museum is an interesting addition and it's a joy to observe the creatures in the game. The Time Trial mode, unlocked by completing the game, is sort of tacked on, but the time-reducing red coins and flowers do add a nice strategy element to the mode.
There are a few flaws that let the game down, though. The level design occasionally ends up not being quite as inspired as the original, primarily when it attempts to directly emulate the original's stages. A particular annoyance is that many mechanics such as some of the vehicles Yoshi transforms into and Poochy were cut, with the substituted Kangaroo and mine carts being not quite as memorable. However, they kept the ever-irritating skiing sections just to increase the difficulty. The music is by far the weakest point of the game. It's rather bland for the most part and although some of the remixes of the main overworld theme may be amusing, the music isn't catchy, a disappointment considering the vibrant tunes of the original.
Overall, Yoshi's Island DS is a nice, challenging platforming game with many great stages and fun gameplay mechanics. At times, its attempts to live up to Yoshi's Island: Super Mario World 2 let it down, but it's nonetheless a solid game that supplies classic platforming for a newer generation.