It’s certainly a personal preference, but I’ll give some insight as a casual Punisher fan:

A character doesn’t need superpowers to be interesting. People can enjoy the Punisher despite him being “just a guy who shoots people with a gun” in the same way people enjoy “John Wick”, “Judge Dredd”, “Taken”, “Jason Bourne”, “Die Hard”, or any movie starring Arnold Schwarzenegger. The archetypal “one man army with nothing left to lose” story is cliched and perhaps “basic”, but can also be written in a compelling way depending on the author. Lots of different authors have written for The Punisher over the years, some being better than others.

I personally think a fun aspect of the character is his understanding that he isn’t a good guy; he (in most continuities I’ve read) hates what he has become and only does it because it’s all he knows. He doesn’t characterize it as “justice”, either. He does what he does as a means of punishment, vengeance, and retribution (and considers it a preventative measure when the criminal is irredeemably evil).

Some of his better stories explore the consequences of this judge-jury-and-executioner approach he takes. For example, killing an undercover cop who had infiltrated a gang that was on Punisher’s hit-list. In that particular instance, he was willing to let the undercover cop’s widow execute him as penance for his mistake. The widow lets him live because she doesn’t want to be like him.