Most of the hate comes from the overly complicated "enterprise design patterns" crap that took over the ecosystem in the late 90s into the 2000s, not the language itself. It's quite possible to write clean, clear, appropriately complex, well performing Java code.
On the plus side, of all the languages I've used Java is one of the absolute best when it comes to long term maintainability of code. This is why it's used so heavily in large enterprises with long-lived business critical code bases. Being the "COBOL of the 1990s/2000s" is not an insult, and as a language it is far superior to COBOL in every way. It's not a bad language to program in at all, while COBOL will make you hate your life.
It's also a safe language unless you break out of the JVM with JNI. It's the first safe language to get huge deployment if you don't count scripting languages. Safe doesn't mean you can't have security bugs of course, it just means you're not likely to have certain kinds of security bugs and stability problems like memory errors.
The JVM is really a fantastic piece of engineering and IMHO represents a whole direction in computing I feel sad that we didn't take. We opted to stay close to the metal with all the security, portability, code reuse, and other headaches that entails, instead of going into managed execution environments that make all kinds of compatibility and reuse and portability problems mostly go away.
The biggest current knock against Java I see is JNI, which unlike the core language is absolutely horrible. The second biggest knock is that the JVM is still kind of a memory pig. CPU performance is great, sometimes converging with C or Rust performance depending on work load, but it still hogs RAM.