Yes it is, check this list for a proof. Those are some games made with Java using The LIGHTWEIGHT Java Game Library (LWJGL). It is a low-level framework, which provides OpenGL for high quality graphics and OpenAL for sounds. It also provides input API. With these you can quite easily get started to serious game development in Java.

I am currently writing my second 3D game as a hobby project in Java, and I just love it. In the past I USED to write my games with C++, but after switching to Java there is no GOING back. Supporting multiple operating systems with Java can be very easy, for example my previous Java game, which I developed in Windows for a year, WORKED in Linux right away and in OS X with only one bug without any need to compile anything on those platforms.

On the other hand, with Java you have couple of problems.

1. Garbage collector. As others have stated, non-deterministic memory management is a problem, and you need to code that in mind.
2. Lack of 3rd party libraries. Most of the available libraries do not support Java. On the other hand you always have the option to call these native libraries from Java also, but it's more work to do so. There are also Java ports or ready-made wrappers available for popular libraries, for example I'm using JBullet - Java port of Bullet Physics Library. On the other hand Java has a huge class library built-in, which reduces the need for third party libraries that are not game related. The lack of libraries has not been a problem for me, but I can imagine that it can be for others.
3. Java is not supported by popular game consoles and there is no easy switch to those from Java as far as I know. On the other hand Android, which is a popular mobile platform, uses some form of Java. This is an option also, but don't except the same Java code to work both on a PC and Android device.
4. Smaller community. Most game programmers use C++ and in my experience often dislike Java. Don't expect to get as much help from others. Don't expect to get a job in game development without C++ skills.

Yes it is, check this list for a proof. Those are some games made with Java using The Lightweight Java Game Library (LWJGL). It is a low-level framework, which provides OpenGL for high quality graphics and OpenAL for sounds. It also provides input API. With these you can quite easily get started to serious game development in Java.

I am currently writing my second 3D game as a hobby project in Java, and I just love it. In the past I used to write my games with C++, but after switching to Java there is no going back. Supporting multiple operating systems with Java can be very easy, for example my previous Java game, which I developed in Windows for a year, worked in Linux right away and in OS X with only one bug without any need to compile anything on those platforms.

On the other hand, with Java you have couple of problems.