Project Warlock can be described as an old school first person shooter with more combat, less maze wandering and a sick soundtrack.
The main campaign is divided into short levels and the player gets to visit a hub area in between stages to heal, buy upgrades and level up their stats, so the player to customize the main character's arsenal over time to some degree. There's also an easy to understand magic system that requires a bit of investment, but it can be just as powerful as weapon upgrades in the right situation.
Stage, weapon and enemy variety is solid. I don't think any designs are particularly memorable as they seem a little derivative in the context of the genre, but the art style of the game is elevated by some great pixel art and animations.
I would also like to add that the levels are generally less vertical than in most classic shooters, and also way smaller. As a result exploration is less important. I personally don't mind some maze wandering from time to time, but I know some people hate it. All there really is to find are secrets, but they weren't hid all that well.
Overall, I really enjoyed Project Warlock. Sometimes shooting monsters with a rocket launcher is all you need to have fun.