Mixed-genre games are often a travesty, but here the Mario platform universe and RPG conventions are mixed brilliantly.
During a party at Princess Peach's castle, Bowser attacks, kidnapping both her and her castle and taking them into the sky. Once again, Mario must set out to on a rescue, and even worse, learns that Bowser has also kidnapped seven Star Spirits and their Star Rod. With a home base in Toad Town, Mario sets out across the world, freeing Star Spirits and slowly gathering a party of eight comrades, any one of whom can battle with him, or join him in the field, at a time. The field screens are very simple 3D affairs, though become very platform-influenced in the end game. Touching an enemy in the field opens the battle screen, where Mario uses both simple hammer or jump attacks, as well as powers acquired from badges scattered across the realm. He additionally can use attack and healing items, and is helped by a swappable party member. Each of the seven Star Spirits grants Mario a special power upon getting freed. Eventually Mario frees all of the spirits, garnering enough power for the final showdown with Bowser.
The biggest strength is the perfect blend of RPG and platforming achieved. It never feels like one genre has been shoehorned into another. With all the towns and inhabitants inspired by former Mario friends and foes, it all feels like a very natural mix, and the nostalgia factor of things from as far back as Donkey Kong adds to the fun. There's a huge number of powers Mario can acquire from badges that are found and/or bought, giving great flexibility in his attacks and defense, as well as stat development. The simple control scheme is ridiculously easy to use, almost belying just how strong an RPG the game is by making you hardly notice that you really do have quite a lot of choices in any battle. Add the large number of mini-quests and side diversions, and you really have a lot to sink your teeth in to.
There are still some mild quibbles. Leveling up allows you to enhance the number of HP, FP (basically spell points), and Badge points, which govern how many badges you can wear. Sadly, they cap the badge points, leaving you to stare at a mammoth list of available powers and only take a few. The game also grinds to a near stop between chapters when you momentarily take the role of Princess Peach, looking for clues in Bowser's castle as to where Mario should go to free the next Star Spirit. The segments verge on stupid, and aren't very fun or necessary. The fact that the cook in Toad Town who can improve items is purely a trial-and-error affair is another mild agitant; a chance to discover recipes would have made her more useful and less frustrating.
The control scheme is flawless, from the classic Mario control in the field to the extremely easy selection of attacks in battle mode. It's just a joy to use. The graphics are classic Mario universe at their finest, and the scores used are neither annoying, nor will they stick in your head all day. The sound effects are very nice, hearkening to previous Mario games when applicable. While some RPGs are longer, you can still get nearly 40 hours in even without being a completist. It's a great game, and even if you like platformers, but not RPGs, or like RPGs, but not platformers, this is a game you'll still certainly want to play.