How "modern" are you interested in? Did it need to be published in the 20/21st century? Would 19th century do?
The Tyndale series (20th cent) is fairly reliable and non-technical. It is also paperback, usually isn't excessively long in each treatment. I mention it for those qualities and because (if I recall) the Genesis volume was written by Derek Kidner, and it is alright.
If I could recommend one, to be gotten used (check the internet)--Robert S. Candlish on Genesis. This is a 19th century work by a Scottish Presbyterian. I first came across it in seminary, and it took me a long time to get my own copy of it (but I wasn't looking either). It was republished in the 20th century by at least 2 different publishers. I think it is superb.
There are other options. Here are a couple more: H. C. Leopold, Lutheran, 2 vols, slightly technical but not overly (20th cent, used market). Robert Harbach, Studies in the Book of Genesis, 1986, nontechnical.
There are plenty of others. I tried to be selective in what I suggested.
[Edited on 9-20-2006 by Contra_Mundum]