Even though the graphics are utterly amazing, with incredible detail, especially on Ecco, there are quite a few glitches which are seen more often than not when artwork like this is being used. For example, in the level 'Roaring Forces', when you get past the long tunnels and into the large cavern at the end, there are holes in the middle of the platform which allow you to escape and explore outside of the level. Also, sometimes Ecco can get stuck in some very odd places and not be able to get out at all until you either run out of air, or quit via the menu. Besides that, some of the levels will be frustrating enough to test the patience and composure of a saint (such as Transfiguration).
However, considering all of the good points in the game, the glitches should be no problem at all. This is one of the best PS2 games I've ever played, with beautiful and realistic movements in Ecco and plants alike, visually stunning levels and landscapes along with the gorgeous soundtracks. You don't have to be a dolphin-lover to admire and love this game.