I'm only a sidecar Trek fan (I have watched every episode of TOS and TNG with various Trekkies/Trekkers I have known, likely woulldn't bother on my own) and the only Trek novel I have read is Enterprise: The First Adventure by Vonda McIntyre (which doesn't seem to be available digitally?).
Occasionally I will look at the books and the ones that tend to appeal to me are ones that explore some side story, rather than dealing with something that would have been covered in the show. So I have Enterprise, the Khan trilogy by Greg Cox, the Q trilogy by Cox again and the Kobayashi Maru by Mike Martin. I also have Broken Bow by Diane Carey, the novelization of the first Enterprise episode (which now that I think of it, gives me
two books that could be described as Enterprise: the first adventure
).