See how it all started.
Usually in Mario games the story is pretty much always the same, but this is not the case in Paper Mario. King Bowser steals a Star Rod from Star Haven, wins Mario with it and of course captures the Princess. The rightful owners of the Star Rod are the seven Star Spirits and they help Mario back on his feet. So starts a quest to rescue the Princess and to get the Star Rod back. Story includes many interesting characters and they all bring some deepness into the main story.
Graphics are really starting to show their age and it´s definitely the weakest thing in Paper Mario. Sound is also pretty modest and they are not up to modern standards.
Gameplay is familiar to anyone who has ever played a Paper Mario game or a Mario & Luigi game on a GBA or a DS. Battles are turn-based and the controls are simple and intuitive. If you can forgive the graphics and sound you can say that this is a great game in terms of gameplay and story.
I recommend that you play in small doses, because the whole story is told through text and there´s a lot of it. After an hour or two it really gets boring. At this point it´s advisable to take a break and continue some other time.
The original Paper Mario is worth downloading from Nintendo´s Virtual Console. It shows how it all started in 2001.