What do you think of novelization tie-ins?

By novelization tie-ins, I mean books that are based off of movie and video game series like Transformers, Metal Gear Solid, and Resident Evil. Here are some examples:

-Resident Evil: The Umbrella Conspiracy
-Halo: First Strike
-Metal Gear Solid
-Resident Evil: Genesis
-Transformers: Ghosts of Yesterday
-Halo: Contact Harvest
-Halo Evolutions
-Transformers: Exodus