I read some the comics after watching the Netflix series. I found the series (at least the first season) to be a compelling story about PTSD and the struggles of veterans. Tom Waits' "Hell Broke Luce" in the pilot was particularly telling.
So I started reading Garth Ennis's Punisher Max series from the early 2000s looking for that theme and I got something way different. Sure there are some hints of PTSD, but revenge is undeniably a central theme- though it is often portrayed as a complex emotion that many characters, not just Frank, greatly struggle with. I'll admit that some of the stories about revenge against crime families or Barracuda are a bit flat, but overall the comic is way more nuanced than violence for violence's sake.
The Punisher Max series has a really fantastic over-arching plot line involving the US miltary and Russia that portrays the Punisher as more than just a vigilante. I cannot recommend enough "Mother Russia" and "Man of Stone". Both have fantastic writing and strongly developed characters. "Mother Russia" has an amazing 4-way chess game between The Punisher with Nick Fury, corrupt US generals, the Russian military, and the Man of Stone. These stories and other ones like "Valley Forge, Valley Forge" also grapple with the trauma of major historic events such as the Vietnam war, the Russian invasion of Afghanistan, and 9/11.
I can't speak to other Punisher comics, but to dismiss the Punisher Max series as just an emo guy shooting people does it a great disservice. There's complexity in the fictional characters and plot that is grounded in very real events and emotions. And it also shows you don't need fancy gadgets or special powers to tell a rich and interesting story.
If you actually want to try to understand the appeal of The Punisher, read Garth Ennis's Punisher Max series. There are places to read it online for free and your local library might have it ditigally.