Great, entertaining and surprising. Albeit everything good ends pretty quick, takes about 10 hours to finish the game.
What made me even more pleased - firearms were not all that useful. With bare hands or some kind of melee weapon Riddick is more robust. Taking out guards quietly and hiding them is the way to success, but for a change of pace you'll also have a chance to drive some mecha units shooting, stomping and blowing up everything on your way.
Add some puzzles just to keep you working, dark humor, good graphics, audio and you've got yourself a game worth playing. Actually it would've been 10, if not for some annoying "errands" you have to run to advance on the plot. Weird enough Riddick had to do favors for some thugs, at least I couldn't find any other way. For example you need something, and prisoner has it - but you don't have an option to beat him up and take it, no, you'll have to do what prisoner wants. And even though you usually have some choice of errands, but I couldn't find a way to manage on my own, hence 9,5.