If you like the demo, then you'll like the full game. It's more of the same.
It's NOT NOT NOT NOT NOT NOT a AAA title though... it's an indie. IF you speedrun it, then you'll beat it in 3-4 hours, but if you really capitalize on the scavenger hunt element, then it should get you at least 6, which is about average. I've read some people on the Steam forums who have said they've gotten up to 12.
Just remember that it's a very old school game in nature. It isn't the sort of game you play once and never install again. No no no. It's meant to be endlessly replayed. The game knows this since it gives you an NG+ mode

. I'm on NG++ right now playing through on insane. It's great!
Plus, Flying Wild Hog needs your money if you want them to make more games! Support the little guy! Nothing pisses me off more than people saying things like "Oh, I guess I will wait for their next game" with regards to indie devs. If you don't buy their current game, then their might not be a next one! Hard Reset is a good time.
Zhukov said:
Hard Reset is very short. You'll finish it in about 4 hours.
This isn't true. Play the game for yourself and stop basing everything you read on reviews. The reviewers had to speed run it on easy since they needed get their reviews out on a timely basis.
Please, stop spreading misinformation.