The best one is hard to name... so I'll pick three. The first one is Legend of Zelda - Ocarina of Time. Awesome game, really nice atmosphere, one of the best soundtracks for a game EVER. And it ages very well. The second one is Final Fantasy 7. The story is second to none and is imo only rivaled by Final Fantasy X (my third game on the list). In my opinion FFX has the best ending of a game PERIOD. I shed very manly tears. And the best thing about it? They're going to make a version for the PS3 in HD!
The worst game I ever played was 'Landwirtschafts Simulator 2011' (Farming Simulator 2011). I was looking for a tycoon game that puts me in the role of a farmer (I'm totally into the whole tycoon game stuff, especially Capitalism 2 and Transport Tycoon) and it was cheap. And MY GOD was it horrible. Worst 5 bucks I ever spent.