I think it has revolutionized the visual aspect of web programming. here's why:
1. Focus on objects and code instead of <tags>
I'm working in a classic asp environment right now, and alot of my time is spent hunting down improper html tags that are messing up the page. With asp.net, the controls do it for you (yes, you may need to tweak, but you don't have to worry about accidentally forgetting to close a table tag or td/tr tag, etc.). With working in a visual medium, you avoid the time to change code, save it, then open it in a browser. for the most part, you have a great idea of what the page will look like as you develop it. Those seconds add up and can make a difference in dev time.
2. Yes, with java you could create a much richer UI, but you can do the same with vb.net winforms embedded within an asp.net page. the point of 2. is that asp.net is NOT meant to rival java. Instead, its meant to move web development to be on par with desktop development: i.e. object oriented languages and benefits, enriched development environments, better database/data access/manipulation, etc.
Sorry, didn't mean to start ranting (why is it that we geeks get so passionate about our tech?). Just wanted to drop in my .02 cents
D'Arcy