Slick, varied and downright fun combat is really all this game is about. Sure, it has an attractive art style and an enjoyable (if somewhat cliché) soundtrack but its core is the 2D beat-em-up gameplay. Be sure you have a controller you can play with as I can't imagine playing this with the keyboard (I used a PS2 controller).
For me, the highlight of Shank is its boss fights. Each one has a unique weakness that you can take advantage of. However, if you want more of a challenge or can't figure out the weakness, you have the option to whittle them down with normal attacks. While there isn't a huge variety in the grunts that you'll fight, I never grew tired of them because you steadily unlock new weapons that reinvigorate things and quite simply, the game isn't long enough to start getting bored. It also helps that you have 6 different attacks, a dodge/block button and jumping at your disposal as you combo your way to victory. There are some platforming bits that got tiring but fortunately the developers were smart enough to keep those sections short.
The story is a very simple tale of revenge that is entirely forgettable but serves its purpose to drive the action forward. The voice acting is equally adequate without being distractingly bad nor anything noteworthy.
Given Shank's short length it's hard to recommend at full price. But on sale or packaged in something like a Humble Bundle it will surely entertain you for an afternoon or two.