I've done that loop a few times when I lived in Fort Collins. Not too bad first day since grades are reasonable, but watch for winds which can make it tough. Walden is a nice place for overnight with camping in the park. Coming back via Poudre Canyon is almost all downhill, so a morning climb to Cameron Pass followed by nice descent. However, summer weekend days can get very crowded in the Poudre Canyon.

If you like that loop, another one to look at is: (1) drive to Laramie and park at the airport (2) cycle to Saratoga (3) cycle to Walden (4) cycle back to Laramie. There is also a triangle ride that can be done: Laramie, Saratoga, Medicine Bow and back to Laramie - flatter but not as interesting.