Sonic Unleashed is my favorite Sonic game, with CD being a close second. Even though it does have its flaws (forced medal collecting near the end of the game, some of Werehog stages being overlong... Empire City was an hour long last time I checked, EGGMANLAND), I still find tons to admire about the game. It's the last game I could name where Sonic Team put in a ton of honest-to-god effort, there's just so much attention to detail in the game that for anyone coming from '06 they'd definitely be stumped. All the townspeople and their conversations, the details in the levels and the hub worlds, and just the visuals overall. It's been seven years and it's still the most beautiful Sonic game to date. That and speedrunning through the day levels are genuinely great fun, I love speeding past everything and even playing the extra levels which are more platforming/rail-based.
As usual for any Sonic game, the music is outright fantastic. Jungle Joyride Night, Rooftop Run Day, The World Adventure, Endless Possibilities, Windmill Isle Day, Eggmanland, Arid Sands Night... I could go on. The characters are also developed reasonably well, and the writing is decent by Sonic game standards as well and the story was nice even if it felt somewhat derivative of Sonic Adventure. I don't care what y'all say either, I'll never dislike Chip.