I was not particularly into the Old Spongebob. I did watch maybe three or four episodes and thought it was clever, quirky and funny, but not something I would watch religiously for some reason. But I know quite a bit
about the new episodes thanks to TheMysteriousMrEnter and his "Animated Atrocities" reviews. And it's not hard to see why they're so atrocious...
In one episode Spongebob decides to get a pal for his pet snail Gary, not realizing Gary is perfectly happy being alone while Spongebob is at work. Spongebob *steals* a strange but adorable looking creature, which he names (ugh) Fluffy Puffy. Fluffy Puffy sees Gary and transforms into a terrifying, hideous creature that tries to *kill" Gary while Spongebob is an idiot and doesn't even notice.
In another episode Plankton decides to commit suicide by lying on the street until he gets run over. Yes, suicide in a children's cartoon. It's because he's terrified of whales because they eat plankton. I think the show has gotten plankton confused with krill, which are tiny shrimp-like creatures.
The Splinter episode. Oh dear lord, the infamous Splinter episode. As someone here has already mentioned a couple of times. Spongebog gets a splinter deeply lodged in his thumb, which swells up and is shown getting full of pus close-up as he tries to hide it from Mr. Krabs, who then just pulls the splinter out, and then everyone gets sprayed with green pus. It doesn't even really make sense since Spongebob gets chopped up into pieces and other injuries but heals from them pretty quickly, apparently because sea sponges can regenerate themselves, so how could a little splinter cause such a mess?
The gross-out "humor" has gotten a lot more cringeworthy and a lot less funny. Squidward gets one of his toenails graphically ripped off, it's implied that Patrick eats soiled baby diapers while in a dumpster, Sandy takes her fur off to take a shower and the fur looks like a dead animal corpse while her naked pink body is covered in bristly hair. So it's really not that surprising at all that so many people don't like the new episodes.