Perhaps this stems from me this time having a bit too much faith in the promotional material that heavily featured Shiho (who really appears only at the beginning and at the end), and that line about seeing what characters who didn't exist at the time did in that day (but in actuality some of the characters just get a really kinda pointless cameo that doesn't really mean anything, and some characters just appear in the montage at the end).
I'm quite certain that both the erratic montage and some of the cameo appearances may not fit continuity all too well, but this is a bit trivial overall. I think the biggest problem is that most of it is sort of pointless. In fact I'm not entirely sure why this special needs to exist.
Japan has been going through an anniversary/nostalgia trend for a few years now. A bunch of old series get new shows and/or movies and/or manga, but those series ended years ago. Making new products of those shows wasn't just celebrating said franchises, but also giving you a chance to once again see these characters on screen, listening to them, maybe making you feel something and hit you in your precious precious nostalgia buttons. But Detective Conan...? It never went away. It's been running in print since 94, with new episodes on TV since 96, with a movie once a year every year since. Detective Conan doesn't have the luxury of giving you one more chance to enjoy these characters because you get them all year every year. And it's a problem, because at least part of this special felt like it wanted to hit your nostalgia with these old moments. Shinichi and Ran may go around establishing their relationship in this special, but this "romance" has been going for 23 years already, so rather than it being "delightful" in the special, my head flips it into "I can't believe this is a plot thread that still goes on so many years later". Instead of reminding me about the fun I may have had with these characters, it just becomes frustrating.
Most of the recreated scenes felt somewhat boring overall. Yes, I get it's called Episode One, but rather than simply pad out the content of the first episode, they could have done something that wouldn't have made it so... samey... like... showing what other characters that didn't exist at the time were doing. Crazy idea, I know.
The ONLY time I felt my nostalgia button was getting pushed was during the montage in Tropical Land with Zard played in the background. This was probably the only time that I thought to myself "this is kinda lovely". I don't know how much it was because of Zard (probably a lot), but if they wanted to press that nostalgia button, well, at that specific point they did it. That said...
I honestly have to wonder how much the new new content and the new old content (movie 4 rehash) truly work with the original first ep/chapter. If you bother to redo something, at least you could reconsider if what you originally wrote even works with the new stuff you add in. For example, after Shinichi and Ran having this M4 scene and the music montage, how much sense does it make that suddenly he becomes completely obnoxious and talks about Holmes and mysteries? Yes I know that's how it originally was, but does that truly work with zero regard to the rest of the content (or hey, maybe in all the dialogue in the previous scenes Shinichi was just as obnoxious and I just couldn't understand it...), or how about Ran crying after the case is closed? Sure it may have made sense at the time, but by now Gosho went back to these characters' pasts various times and inserted various cases since the time they were children.
Most of the cameos felt silly and unaccomplished. Some characters were just relegated to the montage at the end (so they didn't really appear in a new material), the FBI cameo was ruined by Jodie speaking English (way to take everything out of that scene), and I don't even understand the Yukiko and Yusaku cameo being in those costumes. It's like the very definition of the 'member berries from South Park "'member when Shinichi's parents wore those costumes to fool Conan?" "Yeah, I 'member". Again, going on the visuals alone, but it really seemed like the ultimate "remember this was a moment in the manga?" moment. And when such a moment exists only for this sake, it really seems silly.
I guess one conclusion that should be taken from all of this is that a story has a beginning and an end, and If you bother yourself to go back to your beginning many years later, maybe you should do so only after reaching the end first. Otherwise it may just fall flat.