<p>I talked to a few friends who say that Drupal is amazing, and it is a way better than Joomla. What are the major differences/advantages?</p>

The
API
. Every form and pretty much every bit of functionality can be modified via a module that hooks into the API, without having touch core code.  This makes upgrades
much
easier, as your customisations aren't overwritten.
The code it outputs by default is much nicer, as well.