(This info is based on the new S. Platte guidebook.)
Greenville Ave. is an easy route but deserves to be climbed simply because of its aesthetic appeal. Climb the vertical crack to where Optical Illusion begins. Belay off the tree and then traverse the crack below Optical Illusion over to the bolt anchor to the right.
Get down by rappeling or lowering off the bolts. These bolts are the anchor for at least 2 or 3 more routes, so you can easily switch to TR'ing the harder face climbs.
Be sure to bring all your large pro. We used a #4 Big Bro and a #6 Camalot in the wide sections in the second pitch.