I find it annoying that frost magic, when used against us, stacks and compounds the slowing problem. Sometimes I get hit by one Ice Storm and it registers multiple "hits" because of staying in the stream. This slows me to a crawl, as if I were overencumbered, sneaking, walking, and double overencumbered again.
However, the most an enemy can be slowed by our frost attacks is 50% (feels like only 10%), but it seems they can still sprint through that. I shoot multiple ice spikes into a charging warrior, I backpedal and shoot, and he still catches me and hits me. Even if he is a heavy armor wearer and I'm in robes. It is a tad frustrating in that regard. Maybe frost would be too overpowered if it stacked on enemies.