I have stayed in 2 different capsule hotels in Sapporo and my experience was totally different.
One was a new Spa Hotel with very nice "capsules" and a huge bath.
see here
DSCF7204.jpg (image)
and here
DSCF7206.jpg (image)
this place was really nice, you couldnt here alot from the next person, they had a nice locker for the close and the TV was free (even the adult channel). Ive stayed a few nights there and really enjoyed it 2900yen
The only dropback was a club playing music 3 floors away, but it wasnt to bad.
i than decided to try a "real capsule hotel". see here
DSCF7139.jpg (image)
and here
DSCF7138.jpg (image)
wich was 3200yen
The lockers where far to small, you could hear the guy next door snorring, the smoke frome the smoking area came inside the sleeping room, TV was 1000yen extra. The Bed was just long enough (im 180cm) and i didnt have a plug inside the capsule.
The bath was alright, though nothing as stunning as the other place.
Both of them where located right in the Center of the nightclub district and not to expensive, so i would say give it a try! Best would be to ask something like a tourist office because the know the new places (like the first one i stayed).
Have fun
Edit: one more thing, both of them where for men only! There are only a few wich allow woman.