I have said it before, I am a fan, just not a mega fan. I haven't watched every single episode ever made. The basic format of the episodes gets very dull after a while. But that doesn't mean that I wanted to miss out on the arcs that make up the series canon, I just didn't want to see it all. So if you want watch something like this, what do you do?
I've know a lot of people recently who want to start watching or re-watching the anime but nobody wanted to sit through a crazy amount of filler and only watch the episodes with significant developments in them. There has to be a list like this right? With that thought in mind I went about looking for such a list, and I found one. It contains every episode up until XY and it contains list of non-filler episodes.
This list is really only one person's interpretation of which episodes are crucial to the overarching plot, so there are some episodes which say they have a major plot development in them on Bulbapedia, yet, I feel like they really aren't all that crucial to the story. One point I would like to make is that Bulbapedia treats all of Todd Snap's appearances as canon, but in truth he is just there to promote Pokémon Snap.
Kanto original series is almost mental and weird, and while I like it, watching it can also be a tripy experience. If you don't want to watch for only nostalgia then there is that, but the list does a good job at keeping things to a minimum.
There are also a bunch of episodes in Unova because they have some some development in the Team Rocket plot, which could maybe be taken out. They also added a pointer where each of the movies fit on the timeline incase you want to add those into your viewing of the series.
I think there are some episodes that should be added or removed, but the list is a pretty good starting point for new fans as well as old.