All at once Java climbed towards the more secure platforms and did it well. There are few systems around that with such easy to learn twists can give you that much security, but be aware, only a handful of systems are very close to perfection, and none is perfect. Another big leap was the much improved Collections Framework that now gave you a lot of top notch data structures built in. Yes, Collections is a framework but quite a few data structures was added, such as LinkedList, TreeSet or HashMap, that took Java a giant jump from the humble Vector and HashTable to new levels. Not that these were bad, but now you can pick your choice more sensible and they all work together under a few interfaces.
Developers enjoy such stuff.
Some multi media features were improved, replaced or added. Most notably is the Java Sound Engine that was replaced with a much better one. Further there were many improvements on performance and other invisible changes. Or visible ones, such as a much better Javadoc tool that was one of the most visible, and well done, upgrades over the old one. If the former fuss with version numbering annoyed you, be seated before you continue.