If you liked the demo, it's likely you'll enjoy the game though a few of the game's flaws (especially the camera bugs) don't show up as much there. Overall I find it a good but flawed game, but that's going to vary by personal taste.
As to those bleating about it not having enough replay value, I just went through the Ice Forest with my level 33 Champion and it's a different level if you use the "Aesir Teleport" option as recommended; that auto-levels the opposition to your character level instead of using the scripted values. Four freakin' Trolls in mutual support formation, one an Ice Troll and one a Poison Troll... mutter, mumble.
Besides, you can't access big chunks of the world-tree until you've finished at least one run-through and gained the ability to burn away the Nidhog tendrils.
If you have doubts, rent it first. Me, I bought Too Human with some gift certificates and don't regret it.
-- Steve