What Made X-Men Origins: Wolverine One Hell of a Game?

2009's X-Men Origins: Wolverine is a solid action title that actually did some interesting things with its license, respected its source material, and delivered brutal and engaging hack and slash combat that any fan of the Wolverine property would enjoy. And in a medium where a decent movie tie-in – let alone a good one – is such a rarity, one can't help but look at X-Men Origins and wonder- how exactly did it do what it did?