My (incomplete) understanding of the Rules Compendium is that it will work in a way which is similar to d20srd.org - mainly that if you do not know what you're looking for, it is not going to be very helpful, and if you want advice or fluff or anything except for the precise rules-text, it won't be there, or will be inordinately long-winded to access.
(So, you might be able to get the text of a particular Fighter Daily Exploit. Clicking on 'Reliable' will get you to a definition of the word. Clicking on 'Standard Action' will give you a list of things you can do with standard actions' and so on - but learning the game from it, or playing with only the compendium available would be practically impossible.
I could be wrong, though - we'll find out soon-ish when it is accessible!