If you go during a regular day...my Yelp review would be a 2. As with many places on this planet, often the coolest places are trampled by tourism and somehow a bust.
If you go for a sunrise (arrive about 20 minutes prior to the actual sunrise)...my Yelp review is a solid 5 and so worth it! When this installation is void of all people (and void of their selfie sticks and their kids and their liter and their noise!) as it often is at the majestic morning hour of pre sunrise here in the NV desert, Seven Magic Mountains can be moving, meditative, contemplative and meaningful. It swallows you up at that hour and you feel the surreal land art installation (one of the largest in the US) as I suspect Ugo Rondinone had intended it to be viewed.
Go see a sunrise! Experience your private moment in the presence of land art in the beauty of the NV desert!