I'm currently playing the full game and I'm thoroughly enjoying it!
The difficulty level is such a minor thing, and no different than the way Diablo 2 worked where you had to complete the Normal level game before proceeding on to Nightmare and later Hell.
The game as a whole is WAY better than the original Dungeon Siege. The specialty powers work similar to the way the skill trees worked in Diablo 2. And the Summon Teleport is basically the same as Town Portal in Diablo 1 & 2 so you're not stuck walking all the time as you were in DS1. Another thing is that there are ALOT more secret rooms and secret areas than there were in the original, maybe even more so than most other similar games too. I'm one of those gamers that enjoys exploring every nook and cranny of a game, so there's no way I'll complete this one in 40 hours. Heck, while I am close to the end of Act 1(of 3 Acts plus a secret level), I've already logged about 23 hours of fun. I'm glad I bought the game!