Hahahahaha.... that's actually a great question.
Well, I was in middle of a summer binge watching fest - anything anime I could get my hands on. I had recently discovered you could watch episodes online, and it was something my mom hadn't directly disapproved of (unlike Yu-Gi-Oh! and other things available on TV..). She had let me watch Sailor Moon with my sister when I was younger and they just re-ran the first two seasons over and over. (My sister had printed out the airing schedule and everything.. XD) So after previously running through all of Sailor Moon (Some things you should probably just leave unwatched..), all currently available Naruto (that's when Shippuden was fairly new.. >.>;; and I thiiink I gave up on One Piece because the story lost my interest. So I was no stranger to watching suuuper long series. I looked up popular and suggested anime and came across Detective Conan.
Now with books I have a policy: give it three chapters. If it still sucks, I'll stop reading. I had developed a similar rule with anime (I had watched several muuuch smaller seasons of anime that were recent on certain sites) and decided that anime needed three episodes to determine if I would grace it with my viewership.
As an author of tons of stories on Haibara Ai, I could say thank goodness that I gave it that chance. Taking the other point of view with the amount of time wasted purely on a show, maybe I shouldn't have.. XD;
ANYWAY my reaction: I hated it. The first episode confused me a bit. But I could do nothing but cringe at the art. CRINGE. Taking on episode two, there was just more of this arrogant detective brat. He was inconsiderate and inappropriate, and if his head up Ran's skirt was going to be a sign of the 500ish episodes to come (oh how that number has grown), then I wanted no part in it.
Gin. Gin literally saved Detective Conan from being on the "tried it and hate it" list when he wielded his bat and knocked that arrogant jerk to the ground. And then he was a kid. And then there was a plot. A story line. People I started to care about. And before I met Haibara, I was a ShinRan x.x. I sadly spoiled the fun of learning about Haibara through the episodes because there were pictures of her when you search "detective conan" on google pictures XD But she changed the whole dynamic and I love her to pieces.
So in the end, I guess we can thank Gin for knocking Shinichi out so I wouldn't hate him anymore ... Best life lesson ever?