A few details are starting to leak out … the incipit of a piece from Reuters:

Mads Mikkelsen, Gemma Arterton and Alexa Davalos are joining the cast of “Clash of the Titans,” the Greek-god epic being directed by Louis Leterrier.

Sam Worthington stars as Perseus, who embarks on a quest to save a princess and defeat Hades, the god of hell. Matt Manfredi and Phil Hay wrote the script.

Mikkelsen is playing Draco, a skilled fighter and leader of the Praetorian Guard that accompanies Perseus.

Screenrant adds:

Arterton’s character will be “lo” a demi-goddess who Perseus falls for (although I’m guessing the romance doesn’t work out). The character is a new addition to the story and did not appear in the original film – which is a good sign (IMHO) that the filmmakers are really trying to re-imagine the entire concept of Clash of The Titans, rather than trying to re-hash the original. We’ll see how it turns out.

Personally, I think they should get rid of the Kraken … there are enough monsters in Greek mythology they could use …