The Freesat box uses MHEG for interactive services, a similar implementation to Freeview. Sky uses OpenTV (which isn't, because it's theirs). The interactive services you get on Freesat should therefore be similar in look, feel and function to what you get on Freeview.
This blog posting at the BBC is very interesting on this subject.
Fair comment that you can pick up a secondhand Sky box and not pay for any FreesatFromSky set up, but that still won't get you a full range of HD services and it doesn't guarantee you ongoing unencrypted access to its content ...
Another point, in the long term it should be easier for broadcasters to get on Freesat because it won't cost them an arm and a leg to get on the Freesat EPG, unlike Sky which makes a mint out of providing this 'service'.