I've stayed at the Fort several times. I find the internal/external transportation to be more efficient than, say, POR/POFQ where the theme park buses make the rounds. I've been next to the last POR bus stop a couple times, and I can't tell you how many times during "rush hour" the buses were so full they didn't even stop. You can request to be in the loop closest to the Outpost (where all the park buses except MK are) - it's a reasonable walk (maybe 15 minutes tops) and you would only need internal transport to go to the marina for MK or to go around within the Fort.
If you're driving, it's really nice to have your own assigned parking space. You can actually drive to the parks (don't drive to MK though) and not have to circle the lot looking for a space when you return.
Drawbacks? Hmmm . . .well, you don't have room service (not even pizza). You can get takeout from Trails End up by the marina, but there's no delivery to the cabins. If you order from off property, you'll have to meet them at the overflow parking lot near the Outpost, because they can't get into the Fort. So if having your meals delivered is an issue, that can be a drawback. Along the same lines, you don't have a traditional CS option at FW. You have the takeout, and there is a snack bar at the Meadow pool with sandwiches and individual pizzas, but no food court or anything like that. Most people have supplies for quick meals in their cabins, so there's not as much call for that. That's pretty much the only drawback in my opinion. And the peacefulness and quiet of the resort more than makes up for that small drawback.
You will love the Fort in December. The decorations are phenomenal!