Getting rid of all that gravel was the best thing you could have done. I would also remove a large section of grass on the left side of the falls to give you more room to soften and naturalize the stream edges. Since he is also building a freestanding stone wall adjacent to the waterfall, you will need to be mindful of your plantings. Keep with mostly lower ground covers 4"-6" tall with a few taller accent planting amidst the ground covers and dwarf, creeping evergreens. You don't want to obstruct the view of the wall coming up the drive as I can imagine that won't be cheap either and I am sure they will want to look at it. Just one suggestion on rock selection. Try to use bigger boulders in your stream banks with a restrained mix of smaller ones, especially when making a turn in your stream. Larger boulders will make your job of envisioning the final look and execution much easier. They also look much more natural than alot of smooth river rock eggs along the banks. Looks a lot better though, good luck.