First of all, here's what I loved about the game - the music, the humour, and the view. The game features 107 tracks from 75 different Heavy Metal bands, all the original bands doing their own music. This alone was one of the strongest features of the game as I loved being able to switch between songs throughout and the music added a really fun dimension to the game (which is inspired by Heavy Metal lyrics, imagery, and album covers). Secondly the game had a great sense of humour, adding a fun dimension to an otherwise standard action game (it sort of felt like Legacy of Kain: Soul Reaver to me, but instead of being filled with grim intensity, enjoyed poking fun at itself.) Finally, the graphics are just freaking amazing - speaking as someone who has never played a PS3 game before this one, I cannot stop commenting on how beautiful this game looks.
The negatives can mostly be tracked back to my inexperience with more recent games: in later levels of the game you end up playing strategist in that you send out squads of your men to attack different armies in real-time, requiring a skill-set I don't have a great grasp of yet. There were a few glitches, but overall I loved how smooth the gameplay felt.
For the $20 I spent on this game, I loved it - it kept me busy for a months worth of weekends, and it's open-world concept (wherein you can follow the main mission, side missions, or explore as you like), allowed me to have a really big sense of control throughout.
Like Jack Black says in the opening of the game, "This is so epic, it won't just blow your mind, It'll blow your soul."