I often see reviews that compare the writing of Peter Straub to that of Stephen King (for obvious reasons) and of Dean Koontz (purely because of the horror genre as far as I am aware). But to me they are illogical comparisons. If you want a contrived plot where man meets woman and they both find salvation from their past horrors through love for each other, read Koontz. If you want to slip into reading something that feels as comfortable as an old slipper, beacuse you've read the same story 10 times before, only in different guises, read King.
However, if you want to read intelligent novels with characters that you care for and who develop over the course of the trilogy, read Koko, Mystery and the Throat - All completely different to each other, yet interlinked beautifully.
I am the first to admit that sometimes Straub's writing can be difficult to get into - it took me 3 attempts over a few years before I was able to finish Mystery for the first time, but now i regularly re read all of Straub's novels (apart from If you could see me now, which is the only one I've not yet been able to get into) and look forward to doing so - to entering the worlds that he creates (even though I am left cold by the constant jazz references!).
Basically, if you're tiring of King and Koontz, finding them too simplistic - read Straub.