Great nice looking tank. If I might add a suggestion even though I am a late bloomer if there is any possibility you might consider turning the heavily rooted driftwood upside down. Giving it the appearance of a tree, then place moss or fern on some of the branches lightly and randomly to give it the effect of a tree. I think it would look even better that way. try planting some micro sword or hair grass around it's base to create contrast.
The hill is nice but does create tension in sight and visual. I would suggest using small slabs of slate to create a natural tight eratic formation of steps or abstract retaining wall half way in the middle and back from the front of tank to the left and extract 1/2 of the sand from the left corner and add a thin layer white sand to the mix...I mixed some playsand and white sand together recently for experimentation and LOVED the lighter color it introduced. you might consider it as the playsand is great, but the lighter contrast makes a big visual impact. I bought some whitesand from petsmart in a 5lb bag; it was expensive but worth it. You can also get pool filter sand that is white and will do the job, but need rinsing, rinsing, rinsing.....so does the petsmart stuff, but not as much.
If you want to keep the rooty-driftwood then maybe a unique rock/s underneath it or a nice full set of lengthy anacharis jutting up from the substrate deadcenter below the wood; acting as an asthetic blenber -like vines. I LOVE anacharis when it grow healthy, but in moderation...they seep alot of oxygen and look beautiful when dark vibrant green. I would however plant some microsword around the base of the anacharis to blend a focal point even with the substrate otherwise it is too adrupt.visually.
"Can I also ask why you didn't use and fert substrate below the sand? Like a mix of soil and red clay which plants love. They're poor roots need sustenance!! If you like that opt...just get some miracle-gro organic plant soil (brown bag)and find some red clay(use sparingly and mix ever so slightly. the iron and magnesium in red clay is highly beneficial to plant growth, but will stir up your PH If not used sparingly or in light moderation.) then which you prob. already know. Place it below your surface substrate.
Not sure if your using CO2; this will aid in plant growth as well. I would advise using a DIY system as the manufactured ones; while offering more control, cost alot more and aren't any more effective than the produced ones. Youtube has a few vids for variants...go simple and safe I say. The Pop bottle ones are great and cheap. You'll need a small diffuser, a gang valve and some tubing though along with yeast and sugar.
Goood luck to you and never stop aquacreating and providing our fishy friends and plants with a stable peaceful, healthy environment to reside in.
but my plants are looking good. I think what my tank needs is a powerhead. It's a tricky tank 
lol
.....sometimes you just don't notice the obvious I guess and after looking a bit harder I realized that the swords that lined the back middle of my tank had grown so much that they are squooshed against the front. 
