The Subaru has several disadvantages off-road, most of which have already been mentioned...
1. ground clearance
2. approach/departure angles
3. poor articulation
4. small sidewalls on the tires
5. no low range
A Subaru will do more than fine in light trailrunning or even in mud and snow. If you try and go on a real trail with lots of rock or depressions, you'll get stuck pretty fast. You'll end up with one (or more) tires stuck up in the air spinning futilely. If you're a little crazy, you can get an Outback places it shouldn't go through the use of momentum and too much speed (don't ask me how I know