I really enjoyed the first part of the event and can't think of a bad thing to say about it. I liked the different areas. The little quests and puzzles to open each area were fun.
The second part though there just didn't seem to be much to it. The only thing that happened there was an outbreak that could've just as easily happened anywhere else.
I can't comment on Corsica because I haven't been there yet and until I came to this post I didn't even know it was open. That brings me to my main issue with the event, I know this wasn't one of the topics but I feel like it's important, the communication about the event with the community is pretty awful. I put off starting Sinnoh for a while and finally started it just after the release of the second area and have been checking discord to see when Corsica would open and there has been nothing announced there about it. Also I have a habit of sitting in help chat and responding whenever I can and the lack of communication before the event about when it would start meant every second question there was "when will the event start" or something similar. I think pinned messages in chat or maybe a little pop up newsletter or something when players login would be really helpful not only with future events but keeping players up to date with patch notes, future plans etc.