I had a blast spinning up J2ME Loader on my phone (it's on f-droid) and playing games I had on my Sony Ericsson W595 back in the day :)

Worms, Zombie Infection, Sims, loads of Fishlab games, a silly GTA clone... Massive nostalgia hit

I expected it just to be the nostalgia, but actually those games hold up pretty well especially considering the limitations of the platform! Certainly they are a breath of fresh air compared to the microtransaction/ads/spin-the-wheel/spyware - ridden games for mobile platforms today.