If you've got some spare time and a need for speed, you might want to check out the latest Humble Bundle. It's full to the brim with various Sonic games, including Sonic Mania, Sonic Forces, Sonic Generations, and my personal favorite, Sonic & All-Stars Racing Transformed.
You can find out everything you need to know by visiting the Humble "Sonic" Bundle, but for now allow me to share with you all of the games and the pricing tiers they appear in. Have a look:
Pay $1 or more:
• Sonic the Hedgehog 4 - Episode I
• Sonic Adventure DX
• Sonic CD
• Sonic & SEGA All-Stars Racing
• Sonic Adventure 2 Battle DLC
Pay more than the average of $7.15 (about €6.28) to also unlock:
• Sonic & All-Stars Racing Transformed Collection
• Sonic Lost World
• Sonic Generations Collection
• Sonic the Hedgehog 4 - Episode 2
Pay $15 (about €13.18) or more to also unlock:
• Sonic Mania
• Sonic Forces
While I'm not exactly a fan of most modern Sonic games, there are quite a few good ones here that I would heartily recommend. Most notably, Sonic Mania and Sonic & All-Stars Racing Transformed.
Sonic Mania should be self-explanatory given that it's a remarkable love letter to the original series, but the reason I have chosen Sonic & All-Stars Racing Transformed is because it might genuinely be the best kart racing game out there - and I don't say that lightly. I've already done a "You Should Try" review of it a while back, so if you're interested in all of the details, I would highly recommend you check both it and the game itself out.
Have fun speeding around and running straight into walls!