Lots of games are a lot more fun if you roleplay them. Forget your meta knowledge, what would the character do? This adds a lot to strategy games as it adds challenge and puts you in interesting situations.

Playing without savescumming is also a good challenge in a bug free game. I try to only savescum for bugs/missclicks.

For MMOs - play through to the endgame with randoms only, no guild/org etc.