You know, I would have to watch it again to form a rock-solid opinion. I had to look up a synopsis online to remember everything that happened.
But from where I'm standing, it seems like a very interesting idea. Skinner's backstory is actually rather touching. He didn't take on the identity out of malice, but compassion, and he was carrying on for a man that he respected. Is that so terrible? That said, I'm a bit put off about how the real Skinner--a bloody war hero!--is told to take a hike just because the town was used to our Skinner and realized that they missed him. Hell, our Skinner respected him, right? But who cares, let's just tie him to a train and ship him off.
All of that balances to a net positive, but I do think it says something that Matt Groening hates it. Ken Keeler loving his own work is not exactly surprising, and the arguments that boil down to "bah, you just don't get it, he wrote what he wanted!" remind me of bad arguments in favor of Family Guy. It's all well and good to say for Keeler to say that it should be taken as an experiment, and seen in that light I think it's probably fine. But who knew that back when it was first on the air? No one. While it may stand up fine as an "experiment" today, he doesn't get to mock the fans and critics that had a problem with the episode messing around with what they knew.
Finally, I completely part ways with episode supporters when it comes to the "it's just a cartoon!" argument. It's astonishing to hear such boilerplate from any animation fan, though it sadly isn't uncommon. Oh, okay, cartoons don't have to be consistent? They don't have to obey internal logic? The writers can do anything they want on a whim because they're making a cartoon? Is that really what you meant to suggest? Sorry, not buying it. If you hate the most current episodes, guess what, that's the kind of thinking that produced them. And it's no argument to say "oh, this is no big deal compared to the crap that comes out today!" If episode A is bad and episode B is horrible, that doesn't make episode A good by way of comparison. Just less awful. No, I'm sorry, have some standards. If you're going to defend it, do it on the merits.
But yeah, to reiterate, as an "experiment" it strikes me as an interesting episode, albeit an imperfect one. Very likely not "really that bad" or the worst episode ever. But I can see why a lot of people would prefer to remember it--fondly or otherwise--and then move on.