I'm fairly new to Dr. Who, just having watched some of the newer episodes, and find Daleks rather, well, odd. The idea seems to be that they probably are cheesy villains by today's standards but weren't in the 1960s, and given that modern Dr. Who does have some really terrifying monsters, they are a bit out of place.
Still, even in-universe it's hard to glean their terror. They seem slow and dumb. Perhaps they're durable but maybe you can tip them over or something. In the scenes I've watched with Daleks the show of course takes it for granted that you, the viewer, are terrified. So, why should I be?