I've been pretty happy with it. I migrated my website to use it and I'm also using it for a new project. I've found that I'm significantly more productive with it than when using React or Angular, since there is two-way binding and very little boilerplate. There is also a material UI binding for it [1], which makes it easier to develop advanced user interfaces. In my experience, bundle sizes with Svelte can be smaller than JQuery, whereas I typically see bundles over 1 MB for Angular and larger than JQuery for React. The framework is also very easy to learn, as there is a full interactive tutorial [2] online and the framework is optimized for development experience.

The only area of concern at this time is that there is no TypeScript support and debugging can be difficult as it often throws exceptions in vendor code if the error isn't caught by the compiler. Despite this, I've found that I am more productive and get less runtime exceptions developing with Svelte than Angular since it is simpler to develop with and does a lot of compile-time error checking.

I have a repository with working scss and IE 11 polyfills [3]. It's using a custom system for authentication, but it is easy to switch out with something more ideal. There is also a branch with svelte material UI installed. I find that Visual Studio Code with the svelte add-on is the easiest way to work with it.

[1] https://github.com/hperrin/svelte-material-ui/ [2] https://svelte.dev/tutorial/ [3] https://github.com/iwalton3/swapi-svelte