Essentially, I tuned in for a few episodes, thought it was a bit too sugary for my likes, and tuned it off. I loved the cast -- Ackles and Padalecki and the great Jim Beaver -- but the stories were a bit loose with the mythology at this point. Misha Collins wasn't on the show yet, nor was the always reliable Mark Sheppard. Again, this was very early, a first season kinda reaction.
Eventually, my wife turned me on to it much later in the run. She had discovered it via streaming, and she encouraged me to go back to it. What we did was purchased a few of those early seasons on DVD, and we binged through them in a variety of sessions. Even though I'd still argue some of the 'lore' is a bit goofy (for my tastes, anyway), I was won over by the camaraderie of the cast: they clearly loved what they were doing, and it was hard to not embrace the winning chemistry.
Yeah, like so many, we thought the show took a bit of time to "find itself" again after Season 5 (the originally plotted 'ending' to the program). I'm not so sure it ever truly rediscovered the strength of those earliest seasons, but the storytelling evolved to the point wherein either you accepted it as it was or not: we did -- at least, we wanted to see where it was all going -- so we hung with it. We're glad we did.
I will say -- briefly -- that I think the show's finale, while good, was the wrong way to go. I'd rather they kept the franchise open-ended to a degree as I think it could've been a great property to revisit in either a continuation later on or a big screen adventure or two; but -- as they say -- it is what it is. The great characters were now reduced to little more than their own mythology ... and elderly Sam's wig was damn awful.
In any event, I'd like to keep the show alive for those who love it, and I'll continue to tinkering with these "On This Day In _____ History" as time permits.