The game is short. It clocked in under 12 hours, including the Downloadable Content. Even for me, and I like to take my time to explore. Case in point: I got the achievements for collecting all of the Light Seeds, and doing the Speed Runs, and still got the achievement for finishing the game quickly. No internet help on them either.
This is good, because the game doesn't outstay its welcome. There is enough game to convey the narrative but not so much as to stretch the gameplay thin. The areas don't feel padded and even fighting the same bosses feels okay because it's been nicely tied back to the story and the level design.
The game is also broken down into manageable chunks that could easily allow you to play it in 15-30 minute sessions. There are four city areas, each with six neighbourhoods. Each neighbourhood is fairly independent and even has two distinct phases: heal and collect. It's to the game's credit that you just don't want to stop playing.