The DJMAX series.
I literally have wasted most of my three year's worth of free time on this game series, but I really really liked it.
Portable 2 had at least 2880 Playcounts.
Portable 3 currently has 1712 Playcounts. Glitches in the game made me restart three times, bringing this game to a grand total of about 2430+.
Black Square had ~1650 Playcounts, but I restarted the game and now have 384.
CE had 126 Playcounts, then I ditched it because it was for beginners and was too easy for me.
I also recently bought Trilogy (~230 Playcounts) and Hot Tunes (129 Playcounts).
All of it is at least 7445 Playcounts for all the DMP games. That isn't even counting Portable 1, which didn't have a Playcount counter.
And considering an average DJMAX Level takes 2 minutes to complete, and that failed levels aren't tallied, I would have easily wasted 250 Hours of my life on this game series alone.
*Awrrrgh....* *grumble* *grumble*