I used and wrote code for NeWS - the pre-curser for Java. I was also at the talk where Gosling admitted the problems it had. In some cases, a lot of features of Java were in response to the problems with NeWS.

NeWS was so awesome when it came out, where you can dynamically change the interface at any time. But NeWS had some horrible bits. As a language, it was very hard to read. If you saw a name, you didn't know if it was a variable or a function. That is, you didn't know if the value would be pushed onto the stack, or if it would pop some values off the stack. Best Practice was to add a comment after each line to indicate what the top of the stack would look like after that line. So if you got lost reading one line, you could figure out what the next line would do. But without it, after seeing three words in a row that you didn't fully understand, you were hopelessly lost.

NeWS (PostScript) was a write-only display model. You could not remove anything painted on the screen. You had to write over it. Adobe had Display PostScript, but that never took off.

And because of the write-only display, NeWS had a hard time freeing resources. Garbage collection was very difficult because of this. You would allocate a white square, and never truly "remove it" from memory. As I recall, a page refresh had to re-interpret all of the code - there wasn't any caching of the window.

Also - the entire display model with postscript-based scaling was CPU intensive, especially if you had a computer with slow graphics (quite common at the time).