I carry a ton of nostalgia for this game, but nostalgia or not, this game is super hella. It's the second entry into the Paper Mario series, and in my opinion, the greatest. It's the perfect sequel; it improves on many features from its predecessor, while adding many new ones, and being a brand new adventure altogether.
Gameplay: It's an RPG. Yep. Now, improving upon its predecessor, your partners have HP meters of their own, you are able to do a counterattack, cooler Star Powers, cooler action commands in general even an
audience that watches/aids/attacks you, and overall a better and more complex battle system than the original. Outside battle, you travel the game's decently large overworld, solving puzzles and finding items and other collectables. The overworld has many memorable and fun places to explore, like Rogueport, Glitzville, Twilight Town, the Excess Express... There's a lot to explore. The NPC's always have witty things to say. Oh, and there are sidequests, too. They can get pretty repetitive, though, and they'll force you to travel back and forth across the overworld several times... This brings me to the biggest flaw in TTYD: the backtracking. Intelligent Systems got pretty trollish with the amount of backtracking in this game, lol. Anyways, that's the only major flaw in this game, at least off the top of my head.
Plot: While the plot is overall inferior to what Super Paper Mario brought to the table (tears, that is), TTYD's plot is overall solid. Here's the general gist of it: Peach invites Mario to go on a hunt for treasure with her in Rogueport. But when Mario arrives in Rogueport... Peach is gone. Yeah, who would've saw
that coming ;p. Anyways, Mario meets up with a goomba named Professor Frankly and his past pupil, Goombella, and they talk about an ancient legend about the Crystal Stars and the Thousand Year Door and yada yada yada. Long story short, Mario and his miscellanious partners go on a quest to find all the Crystal Stars and to save Peach. Meanwhile, an evil organization called the X-Nauts have Peach inprisoned and fight Mario so they can get the Crystal Stars for themselves. Then, secret monster, apocalypse, other stuff.
I find enjoyment from all the subplots in this story. Luigi's quest, all the individual stories of your partners and the settings, etc.
Partners: Damn, was this an improvement from the original. In Paper Mario 64, most of your partners had no personality, didn't talk much, and weren't all that helpful after the chapters where they joined. But man, TTYD's partners were amazing. They all had their own personalities, (occasionally depressing) backstories, even development. And they were all used a lot throughout the adventure! To me, the most memorable were Yoshi, Vivian, and especially Bobbery. Bobbery's backstory is so damn depressing, lol.
Other thangs: Good music, strong finale, witty humor and memorable characters.
Yeah, long wall of writing, I know. I just had to ramble some about this game. It's an adventure everybody should embark on.