If you don't have a good drainage system, no matter what you do, it will be a wash anyways (pun intended)
I have 4 different fields for my horses.
One is a dry lot, sort of corral connected to the barn where we ride as if we were showing, as well as put horses that start to get overweight in.
Secondly, we have another field that's connect to the barn that is about 2 acres, and then two pastures that are 4 acres a piece.
The field with two acres, is the one I had the most trouble with. I had to horses in it, and it was a mess. Mud up to your knees. After creating two ditchlines and putting gutters on the barn, its now as dry as can be, except for when it rains obviously. I don't like using gravel, but in spots where it tends to constantly stay wet, its not a bad idea, but I just use sand or saw dust in most places.
I would check to see if there is anyway to create a good drainage system, even if it means grading some of the land, because lets face it, a 1/2 acre is very simple to keep up with proper maintnence.