This type of game is not typical of the GOG library, being a bit (okay, a LOT) more mindless than most other GOG offerings. Therefore, make no mistake that this is an arcade-style shoot-em-up in the vein of the "Ikari Warriors" or "Gaultlet Legacy" arcade games you used to pump quarters into back in the day.
The object is pretty simple: blast the bad guys, pick up power-ups, and proceed to the end of the level, and face off with a few "bosses" along the way.
The graphics are serviceably great, holding up very well considering the game's age. This game would look right at home on the Playstation 2 or similar console. The 3D third-person perspective works, and I have yet to run into any major camera-positioning issues.
The real problem with this game is the controls. Your character has separate controls for moving and shooting (and even strafing). You can move in one direction while firing in another, making the controls a bit hard to adjust to at first. The best solution is to have a dual-analog (or digital) joystick controller with several buttons. Playing by keyboard is very difficult.
Overall, though, for the price GOG is asking, this is well worth the price for the amount of arcade-style fun you'll have with "The Expendables." Face it, if this was an actual coin-op machine, you'd have probably pumped more coins into this one than you'll spend downloading the GOG version!