The first year or so sucked

Beavis and Butt-Head's voices were wrong (especially Butt-Head's), their lingo was wrong, and their personalities / way they interacted with each other was wrong. The dynamic of Butt-Head being the leader / Beavis being the sidekick wasn't really apparent yet; they always called each other "dude," sounding like cheap knockoffs of Bill and Ted, and they weren't funny; just crude. There wasn't much, if any, of the clever writing that made the later episodes so funny.

Some of the funniest parts of the show were when Butt-Head would confidently "correct" Beavis, e.g.:

Beavis: What did people do before they had TV?
Butt-Head: Don't be stupid Beavis, there's always been TV! There's just a lot more channels now.

There was nothing like that in the early episodes.

Fortunately I first started watching the show during the second year when it had already pretty much settled into its final form (1994 / 4th season). Some of the first episodes I saw were "Cow Tipping" and "Beavis and Butt-head's Island," which were hilarious. If I'd started watching during the first year I probably would have dismissed it as a stupid show and never bothered to watch again.