For every dull moment there's a blistering set-piece with a brilliantly orchestrated piece of ear-burning metal. Or an amazing view to gaze at on the world map. Or a celebrity cameo to snigger at (including Lemmy, Ozzy and Jack Black's partner Kyle from Tenacious D). Or just something else to laugh at. The story is great, the characters are likeable and it's utterly unique. It's just a great shame the core mechanics here are so disappointing.