Well you have all of the objectives/collectibles in the levels. Then you have leaderboards if you are into that kind of thing. There is also a new game+ mode. A lot of the time there are different ways to go about things in the levels too. So overall I would say it has pretty good replay value, especially for an arcade release.
A Valley Without Wind - Dynamic RPG from Arcen Games! http://www.arcengames.com/w/index.php/games/avww-features
Thinking of buying this. But I heard it's only about 6-8 hours.
I tried the trial and freaking loved it. And I could definitely see myself playing through that single level multiple times. Especially if I had more gear.
How's the replay value on the rest of the game?
Id say the replay value is pretty good. There's quite a lot of levels, and they're all really big and open ended.
Then you've got the upgrades. You unlock new abilities and equipment using points that are awarded for completing secondary objectives, reaching certain scores and finding hidden scrolls. There are nine of these points available per level. Three for each three different scores (kinda like bronze, silver and gold. Get the highest score and you get all three points) another three for completing the three optional objectives in the level, and a final three for finding the three scrolls hidden throughout the level.
The points and upgrades are persistent too. So if you unlock an ability or new piece of equipment you can go back and use that on earlier levels, which will obviously make it easier to get a better score. At lot of the upgrades open up a ton of new ways to complete each level too, because you'll be able to manipulate the enemies in ways that you couldn't the first time through.