There's plenty of lists online that'll give you a good rundown of the popular ones, but my absolute favorite is a hidden gem called Steambot Chronicles. It's got so many different things to do packed into it, from fighting with giant customizable robots to playing a bunch of instruments with unique rhythm mechanics, to hustling pool. Plus the storyline splits based on dialogue choices you make, leading to a few different endings including a couple where you join the bad guys. It's just a really fun game that I've played more times than I can count.