To begin with a short and sweet definition: Dreamfall is the sequel to Funcom's The Longest Journey, first released in 2000.
It was a welcome addition to the genre of adventure point-and-click games, and was a hit worldwide.
Dreamfall, the long anticipated sequel, was released in April 2006.

In the TLJ games, there are two worlds: Stark; which is the (futuristic) equivalent of the world we all know, and Arkadia; a more medievil world of sorts, with magic and talking creatures of all kinds.
Dreamfall begins in Stark, in Casablanca, year 2219. You take the role as Zoë Castillo, a young girl recently on a break from her studies towards becoming a bioengineer like her father before her. Right now, she's just living at home trying to figure out what to do with herself. She has recently broken up with her boyfriend, Reza, with whom she still remains close friends.
Strange things start happening around the world, caused by what is known as the static - an interference on the wire, affecting television, the internet, cellphones etc. For Zoë, things get even stranger. She begins seeing a little girl on random screens in her home, around town... A little girl in a white landscape, with a slightly creepy-looking house in the background. And she talks to Zoë.

Find her. Save her. Find April Ryan. Save April Ryan.

Ignoring these visions, Zoë goes on to help Reza out by picking up a package for him. This trivial event soon throws her into an adventure beyond her wildest dreams - an adventure spanning two worlds, filled with villains and unexpected friends - as she journeys to find out what is happening with the static, and who the little girl is.

Zoë Castillo: Zoë is a 20 year old girl living at home with her father, Gabriel. Her mother is deceased, she's broken up with her boyfriend, and is taking a break from her studies. All in all, Zoë is at a crossroads in her life, but she has no idea which way to go, or which ways are even there for her to take.

April Ryan: April was the main character in the first installment of TLJ. She was once what is known as a Shifter - one that is able to move between the two worlds at will. Now, she has lost that ability. She's with a group of people, rebels, rebelling against the oppression of the magical people in Marcuria by the Asadi, who have come to bring their religion to the Marcurians. April's primary concern is getting Marcuria back to the way it was: free for everyone to practice magic and religion.

Kian: Kian is an Asadi high warrior, an Apostle, who is sent to Marcuria to root out the rebels and bring the Asadi way of life to them - by killing those who oppose it too strongly. He serves his mistress without raising any questions, without ever doubting what he is doing and why.

Coming.

Where TLJ was a purebred point-and-click, Dreamfall has taken the step into the world of 3D movement. Your character is controlled by using both mouse and keyboard, or a gamepad.
The point-and-click mentality is still there, though. The game consists mostly of puzzles where you have to use what items you may have, or aquire the items you need to solve a puzzle. As in all these kinds of games, it is truly amazing what can apparently fit into a jacket pocket.
What really drives the game, though, is the element of conversation. When in a conversation, you'll be presented with several choices of how to respond, and this will shape the events following the conversation.
Another new addition to Dreamfall is that of fights. You're engaged in a fight if, for instance, you choose the "wrong" response in a conversation, or you walk too close to that bloodthirsty sleeping dog. The fighting is mostly like we know it from older games like Street Fighter - mash mash mash the buttons, and hope that you win.

Would you like to read more about Dreamfall? Then I strongly encourage you to check out the official homepage.