Trust me, when it comes to games, this one is anything but mediocre.
The game also has items not found in regular Pokemon games, and some common items that have different effects. Such as the Oran Berry heals 100HP in this game, while in the regular games it only heals 10HP. One of the new items is a Blast Seed. It can be eaten and inflict damage to whoever is in front of you, or you can throw it and it'll either hit an enemy and inflict damage, or dropped on the ground. If an item fails to hit a Pokemon, it'll fall on the floor right under the Pokemon and they'll pick it up on their turn.
Apples are also new items that are very important. They fill your belly when you get hungry, and if your belly is empty, you'll slowly lose HP till you faint or you fill it up.
As usual, you can only learn four moves and hold one item, but you can only carry 20 items in your bag, so you have to be careful what you bring.
TMs are also in this game, but there are some new ones that you may never see in the other Pokemon games.
I think that covers up most of the boring, yet important stuff, so why don't we get to the storyline?
At the beginning of the game, you're asked to take a test. These are questions about you so they can determine what Pokemon you'll be. Once you take the test, you can chose a partner Pokemon and give it a name. When that's done, the storyline will take off. First, all you see is black and some text. When the darkness fades, you'll see two Pokemon, you and the Pokemon you chose earlier. S/he'll talk for a bit than ask you your name. Once they mention how funny your name is, a Butterfree will come by and ask for your help to save her son. You go into Tiny Woods, beat up some Pokemon, go through 3 floors, and you'll see Caterpie and you rescue him. You go back to Butterfree, she'll thank you, give you some items, than leave. Your partner will take you to his/her home and tells you that you can live there(while s/he apparently sleeps right in front of the doorway) and will ask you if you'd want to start a rescue team. Of course, you have to say yes. And thus, the story begins!
The beginning might sound a bit boring, but you'd have to play it in order to understand how much fun it is. It's a bit harder than other Pokemon games, but it's a lot more fun in my opinion.