Well, completed it last night, all but about 4 chests open, probably took me something like 18-22 hours.
Second half of the game is a massive disappointment, for one it's not "half", it's about 2 hours of faffing about and making choices that are either "lovely and nice" or "evil and nasty", keeping your promises or stabbing people in the back, there is no middle ground for the majority of the big choices, you occasionally get a "Leave it like it is" choice but this is only for little things. For two if you make nice choices you have to grind to gain money to avoid massive casualties. I took the "good" path, not only is is boring but it's unrewarding, unless the occasional villager saying you're awesome is enough for you.
The "big nasty" is a let down, you get maybe 2 glimpses of the actual big bad and apart from that it's just some shadow's that die in 1 hit, there is a brilliant intro to it at the start of Aurora (which is an incredibly short part of the story I might add) and then they just shoehorn it in as the big evil you must face. I don't count Logan by the way, complete the road to rule and you will find out why, basically the game lies to you.
Once again the "final boss" is massively uninteresting, however it pips fable 2 in that it actually involves fighting.
All it all my expectations were clearly set too high.
Let me clarify my position here by saying I very much enjoyed my ~20 hours, it is a very good game, however it could (yet again, go Lionhead) have been allot better.
I will make one final point, it is far too easy. You acquire more than enough health potions to deal with the few annoying (not hard) such as the grenade tossing merc's who seem to be basically designed to waste our time and if you get mobbed, chug a summon potion, kick back and snipe the buggers whilst they are kept busy.
The game contains no challenges, moral or otherwise.