Unless you're playing on hard, the difficulty evens out pretty much when you get to Gran Soren. From then on the game isn't really challenging at all. Even on Hard, once you get past the Wyrmhunt quests the difficulty essentially becomes the same as normal. The difficulty balancing is probably the biggest fault of this game. The only way to up the difficulty is to handicap yourself by not using pawns, but that takes some of the fun out of the system..least for me, I loved seeing others' pawns.
Treasure in the game is probably the second biggest fault lol. The loot is randomized and meant to be farmed, but truth is you can pretty much always get the best shit from vendors. By the time you get to Everfall or BBI, the loot is still randomized and you're slowly running out of stuff to gear up for anyway.
I did all the quests before the Dragon and was around 60 when beating the first half of the game on hard. I'm fairly sure anything above 40 will guarantee you beat the game without issue. The game is very good, but nothing quite captures that awesome feeling of the first 10 or so hours when you have to fear shit like those bandits on the way to Witchwood. That feeling disappears pretty soon.