This is a summary of the excellent Wikipedia article about the Java version history. It is highly selective (and biased on what I know and use), otherwise it would simply turn out to be a copy of the article.

The bold parts are what really brought the language forward as a whole. As you see, not every release has bold parts.

Java 11

^{JSR 384, what's new}

Language changes:

• Local-Variable Syntax for Lambda Parameters

Library changes:

• JEP 321 Http Client standardized

Java 10

^{JSR 383, what's new}

Language changes:

• Local variable type inference (var keyword)

Java 9

^{JSR 379, what's new}

Language changes:

• further continuation of Project Coin (small language improvements)

Library changes:

• Java Platform Module System (jigsaw)
  • modularization of the platform itself
  • makes modules a first-class citizen meant to replace the messy classpath with modules with real dependency information

Other changes:

• People seem to have gotten over the 1.x naming convention, almost no one calls this "Java 1.9".

Java 8 (a.k.a 1.8)

^{JSR 337, what's new}

Language changes:

• lambda expressions (JSR 335, includes method handles)
• continuation of Project Coin (small language improvements)
• annotations on Java types

Library changes:

• Improved Date and Time API

Java 7 (a.k.a 1.7)

^{JSR 336, features and enhancements}

Language changes:

• Project Coin (small changes)
  • switch on Strings
  • try-with-resources
  • diamond operator

Library changes:

• new abstracted file-system API (NIO.2) (with support for virtual filesystems)
• improved concurrency libraries
• elliptic curve encryption
• more incremental upgrades

Platform changes:

• support for dynamic languages

Java 6 (a.k.a 1.6)

^{JSR 270. features and enhancements}

Mostly incremental improvements to existing libraries, no new language features (except for the @Override snafu).

Java 5 (a.k.a 1.5)

^{JSR 176, features and enhancements}

Language Changes:

• generics (that's the big one)
• annotations
• enum types
• varargs, enhanced for loops (for-each)

Library changes:

• concurrency utilities in java.util.concurrent

Java 1.4

^{JSR 59}

Language changes:

• the assert keyword

Library changes:

• regular expressions support
• NIO
• integrated XML handling

Java 1.3

Mostly minor improvements, really.

Platform changes:

• HotSpot JVM: improvement over the original JIT

Java 1.2

Language changes:

• the strictfp keyword

Library changes:

• a unified collections system
• Swing as a new UI-System on top of AWT

Platform changes

• a real JIT, greatly improving speed

Java 1.1

Language changes:

• inner classes

Library changes:

• AWT event changes
• JDBC, RMI
• reflection

Java 1.0

Initial release, everything is new ;-)