>>22729
Unleashed is certainly more like the Adventure era than the games after it, but obviously it started the new style of gameplay, and it is also the first main game in the series to really have nothing directly to do with any previous entries. Tonally, it's lighter than all previous entries as well, even if not as light as the games after it. It still has more of a story than after it, but less than before it. It's a transition, at the very least, but given that the new gameplay starts here, and it's the first to have a story doesn't require you to play any previous entries to fully understand it, I'm comfortable placing it firmly in the "Modern" camp.
Now if I want to complain, then I'll point out that Generations puts '06 in the "Modern" era, and that's fucking bullshit.
The Werehog might feel like a Heroes/Shadow style gimmick a bit, but in retrospect, it's much more of a Classic Sonic style gimmick. A second gameplay style that is still technically Sonic, because they wanted to cater to "fans" complaining about too many playable characters, but did it only by a technicality. It almost feels spiteful. Like how the same "fans" were complaining about how "Classic Sonic never had a story!" so they made Sonic's story in '06 literally be about saving a princess over and over again, like Mario.