So, I finished this:
and this:
yesterday. Holy crap, did Riven have a good ending. And The Book of Atrus added a ton to being immersed in the whole Myst universe, as well as the plot and attitude of the characters involved in Riven.
The actor that played Gehn was wonderful, though I thought that Catherine was described as darker-skinned in the novel than the actress that portrayed her in Riven. Either way, both were fantastic.
I should have waited until today to finish the game, though. 4AM is a wee bit late to go to sleep. Heh.