There is no question that this is one of the best commentaries on Genesis today. This commentary is one of the essential starting places for research on Genesis. His interaction with critical views is thorough, though if you have a problem with all forms of source criticism, you will definitely find yourself disagreeing with him in many places.
However, Wenham is no skeptic. Many times in both volumes he points out places which clearly point to the antiquity of the text. He clearly holds a high view of the historicity of Genesis, as can be seen in his interpretation of the mention of camels in the patriarchal narrative (he sees them as a 2nd millennium luxury, rather than a historical anachronism). There is also extensive comment on the broader literary dimensions of Genesis, such as palistrophic and panelled structures, which highly suggests, at the very least, a high degree of editorial activity, so as to make source/form/traditio-historical analysis virtually irrelevant, and you get the sense that Wenham is on board here. I can't think of a single place where he allows source criticism to derail his exegesis. He clearly is treating the canonical version.
The only place that conservative readers may find troubling is in his treatment on "The Religion of the Patriarchs." If you are familiar with his other work, you know what I'm talking about. Wenham believes that there is good evidence that Yahweh of the Old Testament was earlier worshipped as El, head of the Canaanite Pantheon. One line of argument he uses, for example, is that Baal eventually replaced El, and is presented in the Bible as one of Yahweh's big "contenders." In this respect, he is very similar to F.M. Cross.
When all is said and done, however, Wenham is definitely a 5-star commentary. The good pastor/student understands that he must read critically, not swallowing, hook-line-and-sinker, everything is put in front of him. Nevertheless, both volumes by Wenham are well worth the money you pay for them, and will pay for themselves in edification and knowledge gained.