On the original topic, I just finished Twilight's End, and thought it was quite good. Oltion did a good job of making it sound like he knows his science (understand, I don't know jack about science, so all the matters to me is that the author "sells it," that is, makes me believe he knows what he's talking about). He poses an interesting problem and then implements a lot of mini-conflicts along the way to ensure it never drags. Even so, it wasn't white-knuckle excitement, it wasn't edge-of-your-seat, but it was still pretty entertaining and interesting.
The other thing I liked was how he posed a theoretical philosophical problem (whether or not they should spin the planet) and representing both sides of the argument fairly (even the "idle rich" came off looking like they might've been right, though with dubious motive). I really like it when a fictional story poses a moral or philosophical problem, and then represents both sides fairly instead of just making out one side to be a stupid, one-dimensional antagonist (something that I think Boston Legal usually does very well, also). It's also interesting when it's a purely hypothetical argument; in the real world, I'm pretty sure we'll never have to have the debate that went on in this book, but it's still fun to see well-reasoned arguments from both sides, and it's nice because you don't feel emotionally vested in one side or the other (I thought X3 did also did that quite well). Anyway, just a little review while the book is still fresh in my mind. I'd definitely say that qualifies as a lesser-known TOS book; it won't be remembered as one of my favorites, but it was entertaining enough.