I'm almost done with Halo, so I'm going to try to finish one more game before I leave. Here is what is on my to play list:

Final Fantasy 9
Final Fantasy 10 (starting the 19th)
Grandia 2
Shenmue
Shenmue 2
Chrono Cross
Dragon Warrior 7
Lunar 2: Eternal Blue

I'd prefer one that won't take 40 hours to beat, maybe around 20. Which should it be?

If you only have 20 hours, I wouldn't recommend either Final Fantasy game. Those really require quite a few hours in order to explore the entire world and get the maximum enjoyment.

I'd pick Shenmue (why play the second without playing the first??)