Web Banner - is primarily an idea. Not super animation and super effects. A correctly designed and implemented a metaphor. What gives a simple button energy to click, bang on it and want.

What is a good web-banner? Minimum of words and information, and a maximum of emotion and action.
All of that is instinct: eat, sleep, rest, quarrel, laugh, argue. Desire to express themselves, or vice versa: read, see a lot.

Still - it should be beautiful. Click on a beautiful not forbid. And briefly. Catchy advertising message, the provocative slogan, simple and memorable message: "Alo, a UFO?"

Corporate identity - for those who want it to be recognizable. Subject animation (nice, tasty, unobtrusive and safe). Story, because in animation, as in the theater should be an event and its history. Should vistet gun, which should shoot.