I actually ran the half marathon here last year, which is held on the same course as the marathon (that consists out of two laps of 21K). The slower marathoners are being passed by the faster half marathoners during their second lap.

The event (with approximately 300 marathon and 1000 half marathon finishers last year) is not very big, but has a relatively longstanding tradition (27 editions) on the Dutch racing calendar. It starts and finishes in the cozy village of Etten-Leur. The course goes mainly through its surrounding countryside.

For the village, the marathon is its biggest event of the year, and there is decent crowd support. Besides the Dutch participants, a relatively large contingent of Belgians also participates each year.

The course is very flat, so suitable for PB attempts, although weather conditions may not be always very good at the end of October in the Netherlands (wind, rain).

If you're looking for a fast, very well organized marathon through the Dutch countryside, without too many participants, but with a good atmosphere, I would recommend this one.