I played seasons 1 and 2 before COVID. All our players loved season 1. Season 2 was more divisive for my play group (same players)... I loved season 2 even more, but the other players disliked it for its additional complexity (more RPG style character-building).
Now a few games into Season 0 (the third game to be released, but technically a prequel to the other seasons) with a different group and it's OK. It's "broader" in complexity as opposed to deeper, meaning it tries to merge several Pandemic subsystems together, like there are both Russian agents and disease cubes (hope that's not too much of a spoiler... it is a Pandemic game after all) but your characters evolve very slowly relative to the past legacy games. The upgrades feel really stingy in comparison so game to game there's not as much growth. The game is overall harder too because you have fewer options at your disposal, like they're trying to confine you to tactical location-based gameplay instead of min-maxing your characters optimally, which was the part I enjoyed more in S2 previously. Arguably the movement tactics are the heart of Pandemic though, so I don't fault them for doing that. The plus side is that Season 0 makes teamwork more critical, as you can't simply have an OP character do everything and take over the game.
A side gripe I have with Season 0 is the theme (set in Cold War USSR). It feels antiquated in tone, like I'm reading some shitty spy novel lol. There's not much of a sense of a threat, narratively, just a bog-standard "red bad blue good" story. Season 2 (post-apocalyptic) had much more narrative freedom and actually felt tense. The Season 0 story by contrast feels out of place, like grandma pulled the board game out of the attic 30 years later lol.
In order of personal preference only, of the ones I've played, favorite to least:
- Pandemic Legacy Season 2
- Regular non-legacy Pandemic with all (or most) of its expansions
