I played so many flash games as a kid, lmao. If it was a game on Cartoon Network or Nickelodeon's websites up until like 2006, or anything that was popular on Kongregate or Newgrounds, I most likely played 'em. Cartoon Cartoon Summer Resort and pretty much any Toonami-branded game were particular favorites, as I recall, as well as games like Bloxorz and the Crush the Castle series.
Something that might be of interest for folks still interested in playing flash games every now and again would be BlueMaxima's Flashpoint, which is a project that aims to archive and preserve as many flash games as possible and make them playable over their client. It's a bit of a hefty download even for their lighter client, but having thousands of flash games on-hand is invaluable when you're looking to nostalgia trip and supporting preservation efforts is always worth it!