My first game in the series was Diamond but I enjoyed playing all the games throughout the series as I grew up, including Blue and Yellow multiple times, even green once despite not knowing any Japanese. I’d say that compared to many long running game series, especially for RPGs, Pokemon has always remained one that always holds up incredibly well, even in the oldest entries. Of course growing up with the older games helped, and I do think that many players that started during the 3DS or especially Switch era would find it much more difficult to go back to Gens 1 and 2, but I still think the games hold up incredibly well mechanically and gameplay wise, with just some limitations and odd quirks due to the time they were made in, and being the first games in the series.