Funimation, in general, doesn't suck. After all, I prefer their dub of Full Metal Panic! to the actual Japanese. Sousuke's voice, man..
But someone died and let an idiot make the big decisions somewhere between Japan and whatever was aired in America. I'm mean. It's just like... somehow they never got the feel of it or something. Although I've been scanning everyone's responses to this, I will disagree about Kogoro. I think their version of Kogoro is about as spot-on as an English dub can possibly be.
I hate the Jimmy thing. I just... why Jimmy. WHY. JIMMY. Sorry, Uncle Jimmy. I just feel that the name has passed it's age. Is that possible? Idk, it just vaguely reminds me of things like Gertrude. Or .. something you call a kid when they're a kid and then you call them their actual full name as they get older..? It just makes it hard for me to take him seriously. ((Harley?!?! We're not even going to start with the many names they've made up for Haibara..))
Conan's voice makes me cringe and Ran sounds almost unfriendly. If you watch it long enough, everyone sounds reasonable with the exception of Conan, for me, that is. But what I cannot stand is how they just decided that "Harley" knows about the Organization just to create unnecessary suspense. It jacks up the entire plot. And since it makes no sense, they just opt to ignore it? Like 'eh, no one will notice :D' I never really watched past that so I can't really point anything else out... >.> Japanese all the way, man. What does it mean?!