Just like in the Sonic Adventure and Sonic 06 games, Sonic Unleashed features multiple hub worlds that players can free roam around and use to jump into levels. These hub worlds, and the characters in them, are honestly one of the best parts of the game, with them all being based on real life locations and featuring plenty of collectibles and rewards for exploring them during both the day and night cycles.
What's also great about these hub worlds is how authentic they all feel, with the characters located in them having new things to say to the player after they progress through the story. There are sun and moon medals to find in each world, Chilli Dog bonus missions to work through, various side quests and minigames dished out and even shops where players can buy food, concept art and collectibles. On top of all of that, as the game progresses, certain characters will begin to mingle, and begin popping up in different continents to where they started the game. This encourages players to take the time to really immerse themselves in Sonic Unleashed's world.
There's just so much value in playing this game than there is in something like Generations, which is obsessed with throwing players from stage to stage.
One of the biggest complaints about Sonic games throughout the years has been just how trigger happy Sega have seemingly been in taking the action away from Sonic and making players take hold of dozens of different characters. It's an issue that still plagues the series even now. For Unleashed, Sega thankfully decided to strip everything back and make the blue hedgehog the only playable character, and also limit the amount of characters in the game so that they could get more out of less.
And that is honestly one of the best decisions the team could have ever made, with the relationship between Sonic and Chip growing throughout the game to become one of the most fleshed out and wholesome Sega have ever made. Tails and Amy turn up every now and again to remind fans that there is a still a Sonic universe out there, but thankfully there aren't annoying levels or sections to slog through with them like in other games in the franchise.
Sonic is able to really stand out as an actual hero in Sonic Unleashed because of the added attention he receives. From his opening cutscene on Eggman's ship, all the way to his transformation to Super Sonic against Dark Gaia, Sonic Unleashed is arguably the first 3D Sonic adventure that actually feels like not only an actual Sonic the Hedgehog game, but also one that captures the best feel of the blue hedgehog with all of his quips, happy-go-lucky attitude and desire to help out others.