As long as it needs to be. Filler for the sake of length never made a game better. I prefer a short, very focused experience over a longer, more uneven one. Some games just don't need to be that long. I mean, one of the biggest issues the Sonic franchise faces is that Sonic Team always feels the need to pad out the length with crap like fishing and werehogs, when they would've been much tighter games had they simply focused on Sonic's game play style. This is something that games like Sonic COlors and Generations nearly got right, though they ended up finding their own ways to pad out time, unfortunately.







