Before I say what I like about Rails though, I will take you through what I don't like just to balance things out.
What I don't like about Rails
Asset Pipeline still does not let you use ES6 Modules.Even at this late stage, one still cannot access ES6 Modules in Rails in a "Railsy" manner. You can either bypass the whole Asset Pipeline or else separate out the JS using Webpack or whatever, but in a standard Rails project, the fact that the asset is generated with unique hash in the file name before the extension pretty much nullifies its use for ES6 Modules which need a static location to store the files. You can probably try putting the library files directly in the public directory, but nowadays a lot of these need to be built first which means some kind of build system needs to be involved. DHH, please get on this!
TurbolinksTurbolinks works great in theory, but in practice, as soon as you try to use some third party code which depends on document.ready, you are up a certain creek without a paddle. Not only that, but your JS will live on in memory between pages and if you are not careful about how you write your code, the browser's memory could end up filling up and slowing the user's experience to a crawl (but this is a problem most SPAs face).
This is really a convenience thing that is only convenient if you don't mind running out of date code. Because the asset pipeline makes it harder to pull in 3rd party libraries and their dependencies, some nice people out there will create gem packages of these JS libraries which you can install into your Rails app and voila! They (mostly) just work! Until you want to access a new feature of the library and the gem maintainer has decided to go on an extended holiday. Then you end up trying to pull it in yourself and find out you need to change all the embedded stylesheet links because of the Asset Pipeline (see above)
What I like about Rails
Wait, wasn't that in the dislike section? Yes it was, but there a number of things to like about Turbolinks as well.
It's very thin
Ruby as a language is a dream to work with and a lot of the functionality of underscore and lodash were inspired by Ruby's Enumerable methods (things like each and first and last and reject and I could go on...). Also the ActiveRecord framework ties in directly to how models in 3rd normal form relate to each other so that when you do have to work in the Rails layer it's quite simple.
The react-rails gem is more or less plug and play. The only problem is the lack of ES6 Module support. https://github.com/reactjs/react-rails