Just got my first Dreamcast what game to play?

Okay, so I finally grabbed a Dreamcast off Doorzo for like $90 (my first time buying from them). NGL, I’m kinda hyped to add this to my collection. The pics look clean, but we’ll see if it’s all cap when it runs.

Anyway, what’s the first game I should cop to really test this thing out? I’ve heard Sonic Adventure and Soulcalibur are absolute bangers, but I’m open to suggestions. Also, if anyone knows where to grab games without getting scammed or spending rent money.