Well, for what it's worth, I'm more than 45-50 hours into the game and haven't even visited the last big map. There are four big maps in the game of the size of Cyseal and a few big dungeons as well on top.
So it doesn't have the size of BG2 (I think that no game will ever be that big again) but nevertheless it's big for a modern video game. I would say 80 hours at least if you don't rush and try to explore and enjoy and read the dialogues and stuff. But it could be 100 hours as well. A lot less if you rush.
Larian is a rather "small" indie developer so it's pretty understandable that theycan't create content for several hundert hours anymore (we don't have the 90s with garage companies anymore...). But I think that if sales are good (and it seems they are) they will make a lot of new stuff for the game in the coming months and with the mod tools released to the public there should also be a lot of user created stuff (think NWN) soon.
