Imagine a D&D game where you weren't allowed to know anything about the combat mechanics. Every spell requires you to cast it 5 or 10 times to figure out exactly how strong it is against which monster and the peculiarities of the spell's effects. Every weapon requires you to fight multiple fights before even figuring out how useful it was. Such a game would be a joke. Yet because GW2 is an MMO, a genre with earth-shatteringly low standards, this is accepted by the player base.
Someone never played Morrowind.
Do you even play CRPGs?
Also that would be a fine fucking game. You act like it's a chore to experiment, when I enjoy it.
Three Points:
1. Morrowind is not a PvP game. Rules in PvP need to be much more rigidly defined than a single player game. If I go outside and play a sport with a friend, we hardly need a few hundred pages of rules and referees to go with it. So there is a lower standard in the first place. Morrowind can be about exploration, but a PvP game has to be clear about the rules of the match.
2. Morrowind still gave a lot more information on most things. All I can think of that was not well-defined was the to-hit formula and the formulas for various misc things like spellcrafting and alchemy. Things like spell effects? All right there and well defined. The difference is that in Morrowind you can figure out how to-hit works in the first 5 mins and then the combat is completely understandable. For GW2 you have to figure out each and every individual skill for each class to understand the combat.
3. GW1 had detailed skill descriptions. GW2 does not. The TES series has always similar mechanics, it isn't breaking any traditions here by hiding anything new in Morrowind. Imagine how bad (worse...) Fallout 3 would be if all skills were hidden so that you could only raise them randomly through stats. That surely wouldn't be hated by the codex, no siree.