Ability to connect a debugger that sanely steps through code without getting lost in a library maze
Get a useful stacktrace that's not just lines of framework wrapper garbage and then an elipses.
Also a few more, which I can usually get satisfied:1 Don't fail silently, ever. Use UTC time in the log, I shouldn't have to say this.
2. Don't replace the default logging mechanism. Your wrapper version with the fancy colors isn't better. It just blocks the versatility and functionality of the actual language logging feature written by the language team who are far more competent than you. Stop that, you don't know what you're doing.
3 Inherit the environment in the process forks. Don't make me manually go in and pass things down.
4 Please Stop writing fancy error handlers. They often have bugs so the generated error will just be from a bug in the error handler thus hiding the original defect. It's a defect, all bets are off.
When they are working right they're frequently HTML/CSS/JS which is terrible for testing, statistics, and logging. Also they won't do the lower level exception throwing of the language that allows it to be caught by a debugger so the tooling breaks. You don't need to do this. It only makes things suck. Stop.
Alright that was cathartic