I usually wear 36-38 pants so i got the large but they were uncomfortably huge.  The waist fit fine and the legs were about the right length but for some reason they make the crotch large enough to accommodate those that have elephantitis on their balls.  The inseam is like 20".  This isn't a problem if you only ever plan to sleep in them, or bum around the house.  but if you need to actually wear these as underwear with normal pants on top and walk around, then a size too large will have a terrible fit and bunch up at the crotch and make you feel like you're wearing a wet diaper.  Not that I would know what that feels like.  Anyway, I got some medium instead and they fit much better.

As long as you get the right size, they are pretty good.  Surprisingly warm.  It is too soon to comment on durability but when they are new they fit well and the ankle elastic holds the legs in place so they don't ride up when you put on pants.  I plan to buy some more.