It seems like a reasonable amount of content to me (especially considering some full games aren't much longer than 5hours these days). As for the beta tag I think it's fair description while it's not all the content and thus bugs out side this region will be missed it's an excellent way to test out the engine, the classes, mechanics and the combat in great depth. I suspect a lot of people are going to play though these quests with just about every class combination they can manage which will give obsidian and excellent feel for the balance, the engine and allow a lot of discussion around how the classes and mechanics feel.
Beta is a very ambiguous term these days I but it is a fair descriptor for this, the engine is or should be near complete as are the mechanics and we will be testing them.
Note for those of you who are complaining about only having 3-5 hours are you really only going to play through using one class for your main character? If note then really it's Nx3-5 hours and if you try all 11 classes and some other combos like trying to solo it or trying the Ironman mode your going to end up spending a lot more than 5 hours in this!