I'm not sure I would call Java simplistic.. It seems incredibly bloated to me especially in comparison to Go and other languages.
With regards to security issues, I was under the impression that since oracle took it over, Java has had prevalent issues that have just been ignored by Oracle. Quick search seems to agree..
I have played with Haskell and really enjoyed the language. Although imperative languages are my bread and butter it certainly gave me a different approach to programming, primarily stepping away from an OO design and love of recursion!
I would call Java simplistic, but for a funny reason: with other languages, you can do things the straightforward way using basic constructs, or you can do things the expert way using a variety of more complex (sometimes user-defined) constructs. With Java, you have to do things the simple way. Sure, you have to define a class with a main method in it instead of just being able to print "Hello World", but there's one less way to do that in Java than in scripting languages.
Haskell is a lovely language and everyone should dabble in it for a while, for that very reason: because it makes you look at programming differently.
You're probably thinking of security issues with the browser plugin? They're... unfortunate, but don't affect the language as it's actually used. Don't write java applets, and as a user, don't install the browser plugin.
Indeed. Java in a sandbox in the browser is pretty much a failure. But there is no Go browser sandbox at all, so I'd hardly say Go is better off here. I guess you look better when you don't make the attempt at all.
Have you tried a modern, expressive, strongly typed functional language like Scala or Haskell? I can well believe that go would be an improvement over Java, but Java's not exactly state of the art these days.