The Mario RPG series started back with the SNES with 'Super Mario RPG - Legend of the Seven Stars'. The series has expanded across multiple platforms, and is largely responsible for the Paper Mario series and the Mario and Luigi handheld series. What sets these games apart from both the Mario franchise games as well as RPG's of other franchises is it's gameplay elements. Where the Super Mario series of games is simply an action platformer with some puzzles thrown in; and most RPG's are a wander around, beat up enemies for experience while telling a pretty story; the Mario RPG franchise seems to be some odd mashup of the two. They have all the standard RPG elements pretty well down with the story telling, standard battle system etc., but they add these unique timing systems to the battle, as well as the ability to approach and attach enemies to get the drop before battle. This system keeps the game from becoming some tedius grind, and actually requires a fair amount of skill to battle effectively.
The Mario RPG games generally take place in The Mushroom Kingdom, usually with some cosmic or magic creating spell that wreaks havoc on the kingdom, usually heavily punishing the toads more than anyone. What's interesting about the Mario RPG worlds, is the standard enemies (goombas, koopa troopas, etc.) are commonly allies here. Not only allies, but in many of the games, they will even join your parties, causing a bit of a goomba vs. goomba mashup. To make it even more complicated, sometimes even big villians (I.E. Bowser in Thousand Year Door) will join up with you for a spell of the game. Only about half of the games start out as 'rescue the princess' as well.
The Paper Mario world is quite similar to the Mario RPG world with a few notable differences. First and formost, everything is made from paper, EVERYTHING. They have bits of the world showing cardboard edges, with everyone being flat as a sheet of paper. As the characters walk around in the 3D paper world, they have to flip back and forth. This also allows for some really unique mechanics, like Paper Mario turning himself into an origami boot or airplane.
In all of these games, everything is extremely vibrant and beautiful. The original Mario RPG holds up today. I also wanted to note, where Final Fantasy VII usually gets the props for being the first full 3D RPG, I truely believe that title belongs to Mario RPG.
The Mario RPG and Paper Mario worlds have a vast array of characters. Massively larger than the standard Super Mario world. You have your standards, Mario, Luigi, Peach, Bowser etc. But with each game comes a boatfull of unique characters to help you along in the game, as well as some pretty imaginative enemies to attempt to thwart your progress. I'm not going to go in depth in the characters or I'd be here for hours.
What really seperates these games from the pack, is they are likeable and funny. Not only are do all the characters have fun and likeable personalities, but with a quirky sence of humor and are willing to poke fun at themselves. You can tell the writers had a blast coming up with the stories and scenarios for these games. Something that I love in any game, is when you know it doesn't take itself too seriously, and these games have that in spades.
I'm going to break up the gameplay into a few parts to simplify it a bit. These games have quite a few variances and have multiple modes from the over-world, battles and in most of the games, include some special mode (which I will really only breafly go over).
The overworld mode is what dominate just about any RPG. What differentiates the Mario franchise from the others, is there's actually stuff to do here. Not only are the games in the RPG genre, but there's a pretty heavy platforming and puzzle solving element as well. The puzzles are usually on the simple side, like 'how do I cross this gap' or 'how do I open this door'. Usually most of the puzzles are on the simple side at the start of the game and grow in complexity as the game moves on (as you learn moves and techniques that add to the gameplay).
The battles are really where the strength of these games lie. To start, you can actually attack the enemies before entering the battle to get a jump on them. When while in battle, you acually have to play the game and have good timing for your attacks to have any affect. Most RPG's, you select attack, and the character does the attack with your standard random dice roll attacks. In most of the games, you also have the ability to react and/or dodge the enemies attacks. If you're good enough, you almost never have to heal in battle. With each character and villian having their own unique attack skills and attack modes, this allows for a massive variety within the games mechanics. Out of the lot, my favorite would probably have to be the latest in the long line of Mario RPG games, Paper Jam. This incorperates features from both the 'Mario and Luigi' games and the 'Paper Mario' games kinda giving this game a 'best of both worlds' play style.
Each game (apart from the very first) have unique game modes to enhance the gameplay as well. The most noteable are the 3D mode in 'Super Paper Mario' and the Dream Mode in 'Mario and Luigi Dream Team'. As there's been quite a few games in the franchise, I don't really want to go into detail, as again, it would make this retrospective far too long.
These are some of the most beloved RPG's in Nintendo's line up. Genuinely funny, likeable and fun to play, these quirky games are some of best RPG's around. I know this has been a bit of a fluff peice, and not everygame is fantastic (I'm talking to you 'Sticker Star'). But they are well worth any praise coming to them. If you've never played any of these games, they come highly recommended from me, and most of the RPG gamer community.