Middle Thompson Creek is a tough uphill ride climbing out of the Thompson Creek drainage. The first two miles in particular will challenge your climbing skills. If you aren't in top shape you'll likely be walking. The last three miles level out somewhat. The trail ends when it hits forest service roads at the top. These roads lead into the Four Mile Creek drainage, past Sunlight and into Glenwood Springs.
There aren't any reasonable loop opportunities with the Middle Thompson Creek Trail. No other roads or trails come back into the Thompson Creek drainage (at least for bikes). It is either an out and back ride or you might think about including it in a shuttle ride. Leave one vehicle in the Thompson Creek drainage and drive the other up into the Four Mile Creek drainage. Ride the forest service roads to the Middle Thompson Creek Trail and enjoy the downhill.