ISDN had much, much better latency than even 56k modems. Modems were around 150ms minimum. ISDN was often in the sub 20 ms range. This made a big difference for chatty protocols like HTTP, telnet, etc.
True, though in those days that didn't really matter except for gaming. The bandwidth was so low and the web going in content so fast that the local uplink bandwidth was usually congested causing delays due to queueing and pending acknowledgements. Switches and routers weren't quite as optimised for low latency either. A lot of local networks were still 10base2 (or 10baseT with hubs, not switches) so collissions added further latency.
What I loved the most about ISDN was the quick call setup. Took like 1 second max and you had a 64kbit channel. 56k modems went through a dialling phase, a connection phase, endless handshaking...
Or gaming. I never got good at quake because of it. IIRC they added hardware compression to the later versions (I think starting at 33.6?) that added latency, too.
