Resogun is a very pleasant game. It looks sharp, plays well, and even packs in a few surprises. Considering it's available for free with PlayStation Plus, early PS4 adopters should most certainly play this game. That said, there just isn't a lot of content here. If you're not interested in replaying levels to compete on the leaderboards, you'll be done with Resogun after a day or two.
It's solid, but it needs a little more meat on its bones.