Just finished reading Doom3 Book 2 Maelstrom last night.
I thought book 2 was pretty good, better than the first book, which was also good.
One thing that disappointed me was Kane's trek through Hell. Once we finally got there, I thought- 'OK, cool, He's on his own now, in Hell, this is where the real doom begins'. Unfortunately however, Kane's journey through hell seemed quite rushed. I wanted pages of him just being on his own, feeling hopelessness and despair mixed with his never say die spirit. Costello did capture these elements briefly, and that stuff was great, the way Kane was just yelling stuff as he blew the demons away in damnation. Also I wish the Hellknight was properly introduced in the book... In someways I think that could have been sited as the main demon since it was on the game cover art. Also where the heck was the awesome Mancubus battle?, the one where the first Mancubus comes out of that huge pipe. That would have been nice.
One of the main things I was looking forward to was reading through the boss battles. The Spider Demon was pretty nasty, the fight and descriptions of it's death were fun to read. The Sgt Kelly-Tank with the BFG battle was great and reminded me of fighting that thing for real, but the absence of the Guardian in hell from which Kane rescues the Soulcube was a let down. The final battle with the Cyber-demon thing was fun, but not as good as in the same battle in the game. The setting of a big hall rather than on the edge of a huge abyss was less ominous. It was pretty harsh how Kane lost his lower right leg at the end after vanquishing the main enemy! Heheh.
As for all the subplots, I liked the UAC behind the scenes stuff with Ian Kelliher and his dad, but the stuff involving the scientists in the Ocean lab was a head scratcher since it all lead to nothing. Perhaps Book 3 will incorporate those threads.
If there is a book three, which I think there will be, it will obviously be RoE. This is what I originally theorized for the new novel series... wonder when dsm is gonna give me that cookie and recommendation? See page one.... :)