I'm far from an /Ice expert, only having used it on a few characters... But just as general impressions, it seems fine on my unicorn Dark/Ice Stalker. 'Not the most attractive set in the game, but I tend to go for Minimal FX any time I can anyway, so practically ANY of the more "in your face" effects are going to get that reaction from me.
/Ice on Sents has already been addressed. I'll just add my +1 to what's already been said.
My Fire/Ice is, by a pretty noticeable margin, the least durable of my collection of Sentinels. If I run her like an "unarmored" blaster, she's fine... But there's no way she can get away with some of the things my tougher Sents do.