Ambition is often attributed to games that a) are expansive in scope and content, or b) go out of their way to innovate and push a series or genre forward. Under those definitions, I would call SA1, SA2, 06, Unleashed, Frontiers and possibly SLW ambitious. Forces sounds like an ambitious game on paper, but its implementation was anything but. I honestly don't get people that take issue with games like Colors being deemed less ambitious, as the very thing its proponents often praise it for is having a more focused (ie: less ambitious) scope, trimming down what they deem as fat (extra characters and play styles, hubs, more complex and cinematic stories, etc.) so it could spend most of its effort on polishing and expanding on the main Sonic gameplay.