ASP.Net is probably right now the most extensive and expandable internet implemented language around.
It offers certain things like OOPs(object orientated programming) because it is based on the C language, it is not restricted to C though u can implement various languages such as Java and also VB to a certain extend!
The beauty is that you can write complete C driven applications and execute them straight from the server, this offers huge advanteges that no other internet language can offer.
php, asp, jsp, cgi are all scripting languages which means that they are executed from the clients machine not on the server(this exludes java servlets, but they are proper compiled java programs). Hence you can tell your porgram exactely what you want it to do. You could write a application such as MSWord but have it completely online driven.
Reality is that .net is great but i requires knowledge of other technologies that most internet developers do not have. I am right now reading through the microsoft documentation which is quite thourough and has a good explanation of the whole deal.
Personally for me I want to learn it.
If u want more info go to msdn.microsoft.com somewhere there you whould find a website that is MS owned which deals with nothing but .net (sample applications), i remember its something to do with a fake shopping mall they set up to sell spyware. its just a demonstration site but it allows u to dl the source and see how it works.
If u are serious about .net i suggest to keep checking the msdn site!
Anyway good luck!