I'm a big fan of high-def 3D and just recently got a 42" Vizio passive 3DTV that works with the lighter glasses that you get from theaters. I've only seen a couple of 3-4 min 3D highlight clips of past ESPN 3D games and thought they looked awesome. Here is one:
College Football 2010 in 3d - YouTube
Generally, aerial camera shots aren't too impressive in 3D because the sense of objects' depth gets seriously reduced. However, when they place cameras at field level and zoom in on the line of scrimmage or the ball-carrier, it looks fantastic. With the close-up shots, the difference between foreground objects and background objects is much more apparent. I imagine that instant replays are more impressive in 3D than live plays.
I've found that 3D entertainment can be pretty variable, and some movie directors are really conservative with the maximum amount of separation that they will use between the foreground and the background. However, ESPN uses a nice amount of natural-looking depth and isn't afraid to make objects and people extend out of the screen a little bit.
There was only gimmicky "pop-out" moment in one of the clips. A former Ohio St. player on the sidelines walked right up to the camera and stuck his championship ring right in front of the lens. It was pretty cool seeing his entire fist extend into my living room. I had to pause it and try to read the lettering on the ring.
Overall, watching the field-level shots just adds an extra layer of immersion to make it feel more like you are actually in the stadium or on the field. Right now, the ESPN 3D channel is pretty sparse with content. I hear they just run the same content over and over on a loop until an actual live-event is scheduled. I definitely look forward to getting it sometime in the future though and wish I could watch the UT/Vandy game in 3D this weekend.