Rather than what looks natueral and what doesn't - what looks good and waht doesn't?
I think iit's harder to pull off a good looking aquarium without the natural look, but if thats what you want to do, then IMO it has too many things that don't match at the moment.
The gravel doesn't tie into the colours or the theme of the background.
I'd suggest you get rid of one or the other - maybe replace the gravel with sand if you keep the background, and replace the plastic plants with something that looks more like cacti?
Or keep the gravel and go for a black or a white background? If you go down this route, I reckon you would need to add some sort of decor in the tank which is strictly non-natural, otherwise it will look like it's just a mishmash of stuff; also the fish will like some cover which in a more natural aquarium is the plants.
Honestly, IMO you should go for what you like, and if that isn't a planted aquarium, don't have a planted aquarium. So long as the fish are happy, and you like it, then ultimately it doens't matter what I or anyone else thinks. So there !!!