I like the uniformity of Java language. I like the "inner class" feature that has to be manually emulated in C#. I also like that I can implement anonymous abstract class-interface ad hoc in Java. I wish that internal visibility in C# was tied to a namespace instead of assembly, like package visibility in Java. Method co-/contravariance in C# is tied to interfaces. I prefer it tied to individual methods, like in Java.

Yes, Java is more verbose to write, but it's easier to read. E.g., == in Java is always built-in equality. In C# it can be overloaded. Equality in C# is a mess (IEquatable, IEqualityComparer, the obscure way in which generic collections "discover" equality on the type...)

Then async/await hack and how it interoperates with Task infrastructure. It's so badly documented it's not even funny. An often-asked question is how to synchronously wait on an async method. The usual answer is "don't do it" like it solves anything. But async methods return a Task and the official examples for tasks tell you explicitly to use Wait() method to wait on a task. Which gives?? (A long story about synchronization context.) Java and Project Loom are doing it right, IMO.

Nullable reference types are another hack. I tried to convert a project to NRTs and gave up, reverted everything. I haven't seen a NRE in years :p NRTs introduce a lot of edge cases, with a lot of syntactic noise to cover them and still guarantees nothing (unlike a proper Optional type would).

Java takes longer time to push out features, but my impression is that when they do, the features are better thought out than their counter-parts in C#.

So right now the only thing I'm unhappy with in Java is streams not supporting checked exceptions. I actually _like_ them and Oracle should have invested in making them more usable in some way. What they did with streams kind of signals that they want to deprecate them in the long run. It's a missed innovation opportunity.