Season 4 is just as bad
Season 1: great.
Season 2: acceptable continuation.
Season 3: insufferably bad.
Season 4: more of season 3 and in some ways worse.
I had heard from usually credible sources that S4 righted the ship that had gone off course so badly in S3. I'm not seeing it. An important aspect of S1 was the balance of time spent developing the adult characters along with the kiddie poos. Since S3, at least, almost every moment has been spent on the kids and their tiresome growing pains with school and romance. Once essential adult characters like Jim and Joyce are now relegated to dealing with absurd and not particularly interesting scenarios like escaping from a Russian gulag. Previously, they were interacting with the kids and trying to unravel the various monster mysterious, an interaction which made all the characters more interesting in a Spielberg like manner. In fact, it was better than Spielberg because this show didn't treat every adult as a dense, insufferable cynic needing rescue from the unspoiled spirits of the youth they sired.
The present kid-centric slant would have been far more tolerable were it not for some crippling problems. For starters, the original kiddiepoo cast has grown older and less charming in the classic Fred Savage sort of way. The college-age looking Will character just mopes around with an unconvincing look of perpetual concern on his face. His brother Jonathan is about as exciting as an unconscious heroin addict. Lispy Dustin has now been completely Fred Savaged. Mike and Lucas were dull to begin with and age hasn't helped any. Nancy just looks really weird to my eyes now, but I know it's in the eye of the beholder. The best characters, Eleven and Steve, are still very good even with the writing haven taken a nosedive. This is a testament to Millie Brown and Joe Keery being far and away the best actors among the kids.
Probably the worst problem is the horrible cast of kids introduced after S1. Mad Max wears every second the bitchy "I'm too good to be here" look and is entirely unappealing (where's Deadpool when you need him?). Billy Hargrove and Eddie Munson are lame caricatures of 80s bad boys and not funny in the slightest. The now obligatory lesbian character, Robin, is shallow and annoying. Her little sideshow romance with her high school bandmate is painfully forced. And the worst stereotypical archetype of the lot is Lucas's sister Erica, whose only purpose seems to be to provide bratty, foul-mouthed comic relief but utterly fails to do so thanks mainly to incompetent camera-mugging acting.
It's a pity this show has gotten so dull. Still watchable, but a turd compared to S1.