Java (via GWT) vs Ceylon

That's Java, so it is strongly typed, and we can use fully the IDE: error detection, refactoring, auto-completion, etc.

Perfect if you have a strong background in Java programming, and need to code for the client side.

Because Java is statically typed, integrated development environments (IDEs) for Java can provide a lot more feedback on errors you will encounter. Java IDEs can give you specific errors in the location where they occur without having to run the code every time. This makes is faster to debug and learn from your mistakes.

IDEs also have extensive auto complete capabilities that can help you learn the programming libraries you are using faster and tell you what functions are available.

Java is one of the most popular languages in industry, consistently ranking either first, or occasionally second (behind C or Javascript) in terms of usage. Polls (see sources below) show it to be consistently in high demand, particularly as measured by job board postings. This makes Java a great time investment, as you will be easily able to get a job utilizing your skills, particularly as those Java applications in production now will continue to need maintenance in the future. It also results in great support for tools and plenty of computer science books, example projects and online tutorials.

Most Java code follows very standardized coding styles. This means that when you're starting out, there are fewer questions about how you should implement something as the programming styles and patterns are well established and consistent. This consistent style means that it's often easier to follow others' example code, and that it's more likely to meet at least a certain minimum standard of quality. This discipline with consistent stylistic standards also becomes useful later, when collaborating on projects with larger teams.

Produced JS is highly optimized, can be separated in modules with lazy loading, can be internationalized while loading only the chosen language.

It has a Web IDE: http://try.ceylon-lang.org/ with impressive demos: http://try.ceylon-lang.org/?gist=bd41b47f325b6d32514a so you can try it without installing anything, and see the JS generation / interop in action.

The compiler prevents you from using a potentially null variable, unless you check it is not null. Ie. it forces you to check a potentially null value before using it.
The type system is strict, but flexible, allowing union and intersection of types, covariant and contravariant types, reified types, etc.
Type inference and union types allows a dynamic programming style, close of JS spirit.

It brings type safety to JS, allowing to define interfaces to existing JS APIs, yet using the dynamic keyword for flexible calls in the JS ecosystem.

Ceylon has reified generics, so it doesn't loose the type of collections at runtime. This makes autocompletion, debugging, etc. first-class. The Eclipse plugin makes it a full-fledged Ceylon IDE, and an IntelliJ IDEA plugin is in the works.

Gavin King, main author of the language, has a great, clear technical writing style, making understandable difficult concepts like variance or sound type system.

The language specification is very complete and up to date; also, the language module is very well documented.

Ceylon has special language-level support for interoperation with dynamically typed languages like JavaScript, and its module system even interoperates with npm.

Ceylon is indeed fairly easy and readable. Of course those ones who know OOP and a bit of functional programming concepts will feel almost at home right from the start.

HTML generation is supported right in the SDK.

If you don't use platform-specific features, you can reuse the same code in your backend server (be it in Java or JavaScript) and in your client-side browser code, for example for storing data, validating input etc.