Undeniably superior to the pitiful 2D platforming attempts by developers around the world but more importantly, better than any other of Nintendo's efforts. That is no mean feat.
Super Mario Bros. 3 and Super Mario World are often cited as Nintendo's greatest 2D platformers ever but Super Mario World 2: Yoshi's Island was a masterpiece which had no faults whatsoever! SMB 3 and SMW's main weakness were uninspired and simple bosses but Yoshi's Island in this category is highly original and keeps the challenge very high.
Of course, a great game needs more than classic bosses and Yoshi's Island naturally features the standard superb level design, gorgeous art work, amazing rotation and scaling effects and an addictive and memorable soundtrack. Add to this bigger levels (but less of them) levels than any other 2D Mario offering and you have...oh the best 2D platformer of all time! Have I mentioned that already?!?
It doesn't matter if you're a new gamer into PS2 and shooty-killy games like GTA and the rest you MUST play this game. No you don't understand...you MUST play it! Go buy a GBA and Super Mario Advance 3 (Yoshi's Island ported from SNES to GBA). Extra levels are a mere bonus to what is one of the finest games ever made on ANY platform.