When I had it my pings were always sub 100 in online games.
The response in surfing the web was just as quick as my DSL is now. There was not the lag in pulling up normal web pages.
Downloading large files or playing video is much slower. That is the limit of the 128k bandwidth though.
I had comparable packet loss that I do with my DSL, which is minimal.
It was rock solid and stable. It was extremely reliable and the connection never varied.
ISDN is leaps and bounds better than dial-up, but is light years behind DSL.
The biggest drawback is the cost. It can literally cost you up to 6 times what a basic DSL connection costs. Unfortunately DSL is not available everywhere.
hope that helps, make sure and check out the FAQ's at the top of this forum.