I know you said "free" but for me the absolutly best Payware Bush aircraft is the Do-27 from Digital Aviation. The flight model is really nice, and it comes with the system modeling/damage modeling/engine wear stuff which requires you to use correct procedures, appropriate power settings and to follow the checklist.
The fact that you will get punished for pushing zero to full throttle like a madman, or for running at full tilt for any length of time makes the flying in tight spots that much more challenging.
And the FM is really interesting - it requires some stick forward pressure on approach (like the real thing) to keep from stalling, it slides and the torque modeling is also clearly felt. with full flaps at 45knots you can do a nice three-pointer - it's actually the first aircraft ever for me that has the stall warning come on just the moment I touch down.