The view was amazing driving from Zion to Las Vegas the only thing I would warn about is thinking that scenic view means ability to get out and take pictures or even drive slow.... The people around me were driving so fast and there was no way to stop and take a picture but it is beautiful and breathtaking
I started in St. George going southwest toward Littlefield, Arizona. This section is just desert country, but after you cross the state line, it's not far to the Virgin River canyon. A short section of the Interstate is a bridge that goes above the Virgin River. (both north and south bound)
Being from the east, we don't have a jaded view of the desert, rocks, hills, mountains and passes that comprise a route like this. We've done it twice, once from Las Vegas to Zion NP, and once from Zion to the Virgin River Casino - a scenic oddity and treat in itself, being part of a large manmade golf oasis in the middle of the desert. Be careful of some crosswinds, and of tandem rig drivers - unless you're used to being next to one in a hilly, curvy pass. Otherwise, a really nice drive.