I am thinking to get this game, are the dialogues all serious and boring such as Fallout 3, Oblivion etc or is there a little humour like in the Neverwinter Nights games?

Also, can you zoom out the camera or can you play only from above shoulder view?

There is quite a bit of humour in the dialog, books, etc in the game. In one situation a bandit demands 'your money or your life', to which you can you can go off on a very funny philosophical debate on the pros and cons of each choice, which confuses and angers the bandit until he just attacks. Once defeated you can find a note he was carrying that is very funny, as well.

There is a free camera in the PC version, controlled by the mouse. The camera distance is linked to the angle you are looking, though, rather than being independent. Looking horizontally, the camera will be behind the character (if not for the (removable) UI at the bottom of the screen you would see your whole character), if you move the mouse back to look down, the camera moves back smoothly to a higher distance and steeper angle, while if you move the mousr forward to look up the camera moves closer and then past your character. Generally the camera would be roughly horizontal, and most of the looking up or down (the extremes at least) reserved for exploring and looting.
You could run around with the camera pointed half down for an angled top down view with a still pretty decent range of sight, but would have trouble in combat targeting ranged opponents.

All games in the Divinity series are marked by plenty of humor! It can get a great deal more silly than NWN. The sorcerer Bellegar is one of my favorite examples.

And just to paraphrase Raze, camera zoom is controlled by moving the mouse toward and away from yourself - you can pull the camera out to a medium top-down distance but combat and interacting is easier (for me) by keeping the camera closer in an over-the-shoulder view. It's not a fantastic system but it's better than being locked in a close view.

It's full of humour - I find it the funniest in the Divinity series so far. You meet a fantastic array of characters, many of whom are brilliantly voice acted and their dialogue is fun - it's a tremendously fun game, even in the serious moments. My favourite is a certain re-built necromancer's love. The way she's voiced is just rofl funny. It's not slapstick tho'. I think Larian get the balance right between the seriousness of your characters mission and the fun elements.

The only thing I would add to Raze_Larian's excellent description of how the camera works is that it is incredibly fluid.

ah ah, brilliant, the humour examples were very interesting! I like atmosphere etc too, but some games are always serious, which bore me to tears. Looks like this game is a must get as it has all the right things. Thanks all

It's no mistake that one of the dozen or so faces shared by all male NPCs looks exactly like John Cleese.

Plus there's a killer bunny rabbit.