The earlier seasons (when Jake was younger) really weren't that bad. There were a lot of funny episodes. The show didn't become hard to watch until the Ashton Kutcher era. He wasn't a good fit and they turned Alan into a complete piece of shyt. He wasn't perfect before, but after Charlie died, they took away all of his redeemable qualities. Almost like the writers were like, "fukk it, let's stop pretending he's a good person.
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I think a lot of people resent this show because it was, at best, a decent sitcom that overachieved and became a massive success. It also doesn't help that after the first few seasons, it was surrounded by way better sitcoms that didn't get the same ratings or money. You could also apply this to The Big Bang Theory.