Some people are going to be unhappy about this but I'm quite happy. These expansions are still cheaper than buying a new sister game/s if they decided to release those instead, and since you can jump right into the expansion content with your current save files, it means that you don't have to play through the monotonous story again. It also means that your old game/s won't just rot on your shelf as you play a newer, better version of it, like in previous generations. I also personally like how it spites people who decided to wait for the newer, better version/s of Pokemon SwSh, only to be told that there was no newer, better version/s and that it was instead an expansion pack lol.
In terms of base game improvement, these expansions are amazing. The most new content added in a Pokemon generation followup was Pokemon Black & White 2, with their new areas and features, and this easily trumps that benchmark, with a fair amount of new Pokemon and formes and allowing you to find over 200 more older Pokemon, bringing up the total of findable Pokemon to over 600, more than any generation I think. Not to mention, that the expansion content plays like the Wild Area, which is easily the best part of SwSh, which is absolutely awesome.
Another good thing is that if you don't want the expansion pass for some reason, then you can still get the newly accessible old Pokemon through Pokemon and trade for the new Pokemon and formes through trade, if anyone is willing to trade their one-off Pokemon that is.
My only issue overall is that I personally like the additional save file that buying the sister game/s gets me, but I will admit that I like how it's cheaper overall and that my older games won't just rot on the shelf like Pokemon SM did after Pokemon USUM came out.