We have not yet done all the Great River Road, but unlike:
Blue Ridge Parkway - Skyline Drive
Natchez Trace
Route 66
Or ..... (we did another that I can place right now)
It is not well organized and signed as such over much of the length and will take some navigational skill to keep track. Actually, that was half the fun. And no, you cannot see water most of the time.
Do not let this dissuade you by any means, it is a great run.
Like 66, how it is handled varies widely by state. Again, just have you charts (maps) handy and be ready to deal with the situations.
If you get there, the Ohio and Mississippi meet at Cairo. If you can get to the park at Fort Defiance, make the stop. Don't miss it because you will be on the bridge and the next place to turn around is a mile across that bridge and back. The sight is amazing as the muddy Miss meats the Ohio.
Matt