The long overdue role reversal introduced some neat new mechanics but fell short of its potential.
While Mario relied on a number of special powerup moves to stomp his way through the Koopa army, I guess the designers figured that since Peach is a girl, she should rely on her violent mood swings. When she gets angry she bursts info flames, which can melt ice, burn bridges, and fuel hot air balloons. When she's sad, she runs extra fast, and her tears can put out flames, cause sprouts to grow, and power water wheels. When she's joyful, a cyclone forms around her which can power windmills, clear out smoke, and let her float into the air (which is a very effective safety net when you miss a platform on one of your jumps). When she's calm, her life meter refills. The first three of these powers are the keys to opening locked paths and toppling certain enemies, plus accessing other hidden areas with various coins and items. It's a nice concept to identify which of your powers you need to use to move on, even if what you need to do is often quite obvious. In addition to that, she has a few abilities that she can purchase or earn, like a ground stomp that breaks blocks and shakes the ground, or using the umbrella to float for a short distance.
Other than that, it's your standard 2D sidescrolling platformer. Peach runs through 8 themed worlds, ranging from your standard plains, forests, haunted houses, glaciers, and naturally Bowser's villa. Each of the areas in the worlds doesn't feel too repetitive overall thanks to its good level design. One may have a maze of doors that you need to navigate, the next has you run ahead of a swarm of ghosts, the next has you rotate the room with switches to get to the exit, and so forth. Each of the normal levels has three Toads locked in boxes that you need to rescue to unlock each world's boss, so you need to keep an eye out for them, or even make a second run through the level if you missed them. Before long you'll know what to look for, however, as you usually have to use one of your abilities on something in the environment to be able to reach them. You can collect coin in the courses, which you can redeem at a store for a limited selection of abilities, increase your health/vibe meters, buy minigame pieces, or unlock musical selections... but coins aren't hard to come by when you figure you can redo some of the simpler courses as much as you want. If there's just one drawback, as I'm sure you heard elsewhere, it's that it's ultimately rather easy.
In previous 2D platformers, if Mario got touched by the enemy he either died or lost his powerup. If he fell down a pit, he died. Here, the game is far more lenient. Peach starts off with 3 hearts in her life guage, with each time she takes damage she loses half a heart. Also if she falls, she gets placed a little bit further back and loses half a heart. If she eventually dies, she simply must start the level over again. There are a few hearts scattered throughout the course that refills your life, which is usually enough. Even if it wasn't, as mentioned one of her powers uses her vibe meter (which drains as each of the four abilities is active) to refill her life meter. Peach can use her umbrella to pick up an enemy, and that creepy little freak can then absorb the enemy to replenish your vibe. If you move over a screen then move back, all enemies you've defeated will magically appear, making refilling your meter a very trivial matter (and a later ability will cause that freaky umbrella to envelop the upper half of Peach while she tries to squirm away for air to refill the vibe meter - now you see why I have nightmares about that unholy umbrella). There are a few jumps and sections that prove to be just as tricky as some of the classic Mario games, but the fact that you have so many chances to get by, and it taking seconds for each attempt, you eventually will. A few of the bosses can be a bit annoying (I found the first world's boss to be one of the more difficult), but ultimately only Bowser himself will likely give you any trouble at all.
Each of the worlds have a nice, colorful, vibrant feel to them, and are rather well done, as are the enemies themselves. The characters seem a little bit above average, they just don't seem as good as other DS titles like Partners in Time in terms of crispness, but they're still rather decent. The music is also vibrant and upbeat, though nothing outside of the volcano level was above the average game music. There were very few voiced lines, the most frequent being Peach's "That was easy!" when she finishes each course (so true, Peach, so true...).
There's more than just platforming here. You can unlock three minigames that make use of the stylus or blowing into the microphone. You can also collect puzzle pieces across the courses (and in the shop) to make a minigame where you rotate and place the puzzle pieces to make a picture of Peach in each of the eight theme worlds. Musical selections can also be unlocked so you can listen to the entire soundtrack as you please, and each time you defeat an enemy it's added to the bestiary.
You're not done when you beat the game, either. Each of the three locations you found a Toad in every level now contains puzzle pieces or musical selections. It's questionable if you'll want to go through each level again for this, though, as they're literally in the same exact spots as the Toads. However, redefeating each level's boss will open up three new levels in each of the eight areas, all of them being a higher difficulty level than the original levels. Difficult, though, is a matter of perspective, as at this point they shouldn't prove too difficult when you factor in all the abilities you have gained throughout the game.
In the end, Super Princess Peach introduces some neat new ideas and has well-designed worlds, but it doesn't leave much of an impression since there's little sense of accomplishment due to the lack of difficulty. However, I still found it rather enjoyable to play in spurts. While I'd probably be upset at the lack of difficulty if it was a console game, the fact that I play handhelds on either a bumpy ride or right before bed made this game somewhat relaxing and an enjoyable way to pass a little bit of time. There's enough extras to collect which, though repetitive if you play the game often, can be a worthwhile diversion if you do a little here and a little there. Fans of the old Mario 2D platformers will like some of the nostalgia this game provides, but will ultimately rank it below most of Mario's adventures. That doesn't necessarily doom the game though, as the Mario titles hold a very high standard.