Got this in the post today and thought i'd do a quick write up.
The plot is that Bowser has found somesort of magic rod on an island and has used it to capture Mario and the gang, aisde from The Princess who was out on a walk. The Princess then meets a talking umbrella (I shit ye not) and they set off around the island to free the mushroom folks and rescue Mario.
The game itself is along similar sort of lines to a regular 2D Mario game. Character movement is more or less the same, you use pipes and doors to travel around different parts of levels, you can jump on enemies to knock them out and you have blocks that contain coins. There are some major differences though.
The first is that you can take a certain number of hits before you die like in the 3D Mario games, althougth there are no actuall lives in the game and you just get thrown out of the level with no penalty beyond having to start it again. You don't have to complete a level to retain stuff you collected in it either, you can quit the level at any time regurdless of whether you've finished it before or not and theres no time limits. This makes the game pretty easy and more of a leisurely stroll througth the levels rather then the sort of running challenge that you normally get.
Secondly, you are armed with the afformentioned talking umbrella in a similar sort of way to Parasol Stars. You can use it to hit things, throw stuff, float in water and all sorts of other actions that are unlocked as you play.
Thirdly, you have the much-derided emotion feature where you have 3 emotional states for The Princess that are selected by buttons on the touchscreen. Each of them gives you special abilities that you use to activate things in levels, take out enemies or reach places you can't normally get to. Making her sad will shoot water and increase your speed, making her angry creates fire and making her happy spins her around and lets you fly. You have an energy bar that limits how much you can use these, which can be replenshed in-level with pickups and by feeding enemies to your umbrella.
The game structure is similar to Yoshi's Island. You get a series of levels in groups that you complete in a fixed order to progess, with a boss fight at the end of each group and the option of playing previous levels again whenever you want. Theres stuff to find in the levels and you get bonuses and extras for finding it, but you don't need to find them to move onto the next level.
The levels themselves are a bit more explorable then they are in an average Mario game as well. The start and end points are always fixed and theres usually just one way to get between them, but the pickups are frequently in areas that branch off a bit (sometimes allot) from the main route and there is also the ocasional alternate path as well.
Theres also a shop where you can use the coins you collect in the levels to unlock new moves, get longer energy bars and collect bonus stuff. You can unlock some mini games along the way as well, which seem to be obligatory in all Mario related games thesedays.
Overall its pretty easy and theres not much original about it, but its worth playing and its passing the time here until the new Mario game comes out next month. Its obviously designed to appeal the female audience that the DS has managed to pick up with the likes of Nintendogs, but that wont stop you from getting entertainment out of it as long as you like Mario games and don't go into it expecting much of a challenge. You might even be able to use it to keep the missus occupied if you have one that occasionaly plays games.
Obviously its a bit difficult to take screenies with a DS, so here a link to some at Gamespot...
http://uk.gamespot.com/ds/action/superprincesspeach/screenindex.html
...and some marginally better ones at a big Mario site.
http://www.themushroomkingdom.net/spp_ss.shtml