Blizzard has released a demo for the console versions of Diablo 3. You can grab it for free via either the PlayStation Network or Xbox Live, and it'll occupy about 1.2GB of space on each format. That's great news, because Diablo 3 is fantastic on consoles. However, the 'even better' news is that--if you decide to buy the full game--your saves will carry over, so there's no need to start afresh.
The demo offers you the chance to play as either the Barbarian or Wizard classes (there are five in the full game), and you can play up to the Skeleton King, who is the first boss character. That means you get hours of play, rather than minutes. You can also play in co-op, both locally and online, and any loot / stats you collect will simply carry over if you buy the full game digitally or from a shop.
Unless you're worried about bandwidth or download limits, we'd thoroughly recommend giving this one a try. Here's our review in case you still need convincing...