We visited a couple years ago while camping at Guadalupe River SP. Rode bikes on the Mission Trail in the morning, then did the River Walk afterwards (ate lunch). We normally avoid the big city stuff on a RV trip, since we're from a large city but we had fun. Like others posted, traffic is pretty heavy there.
Guadalupe River SP was a great stop for us. 3 nights there, close to other attractions as well besides San Antonio, but we simply enjoyed swimming/floating in the river at the park the most.