In terms of overall cushion, the market is fairly divided. Yes, the terrain will be less impactful than running on tarmac, but repetitive pounding on uneven surfaces in a minimal shoe can also be very uncomfortable.
If running on soft terrain, whether mud, sand or other soft ground, a less cushioned shoe which allows you a greater ‘feel’ of the trail may be preferred, but harder trails with smaller rocks and roots may influence a more cushioned choice. I tend to find running in deep mud, which is my typical terrain over winter in the Chilterns, I can get away with a minimal cushioned shoe, as the mud is a natural cushion anyway!
In summer the trails become more hardpacked and having suffered from plantar fasciitis a couple of years ago, I always pick a more cushioned shoe. Similarly, for a long run I will choose a more cushioned shoe to try and reduce the impact on my joints. I am aware that minimal shoes may encourage toe or midfoot strike, but this is a style that requires training in itself.
Also note that the foot swells on long runs, so it may be worth buying a half sized larger (this is relevant for road shoes also, but I tend to find the softer upper on a road shoe have more flexibility anyway).