I remember back when I first bought it. We were poorer back then and buying a new game was a big deal, like once a year. I remember CL, Onimusha, and DMC1 were all I had for a few years. I played CL almost daily for 2 years continuously, then on and off ever since. I was even playing it earlier this year extensively. Back then, we had no choice but to burn our games to the max, creating challenges and developing new strats for years.
Now I've got tons of games but even when I have a huge list of stuff I've never finished, I always find myself popping in CL and getting stuck in that for a while. Once I get the equipment I've got a huge list of videos I want to do for it. I want to put all the knowledge I've accumulated over the years into multiple videos series.
I have the PAL version, but also bought the JP version with its numerous differences.
Runner ups would be, Haunting Ground, Onimusha (Genma), Fatal Frame 1, DMC3, and Okami. Could write encyclopedias on each one.