Supposedly only 20 to 30% of games are ever get finished. That's a big problem because a lot of it is probably due to the game being frustrating instead of fun, it's meant to slow you down.
Yeah, there's pleanty of games which I haven't finished. But the ones I love... now that's a different story. Then, even after 100 hours, you still want more. For me, the best and most gratifying ending was the N64's Turok. You know that you love a game when you see all the credits.
I'm just grateful that I can rent some games, because a lot of them are utter crap. Gamestop has their gameplay guarantee, where if you don't like a game within 7 days you can return it for a full refund. I'll give some games a whole hour or two before I decide whether or not it's worth playing. If they're not they'll usually be returned the next day.