I agree with the other reviews here, the only thing I would like to add that you really should play this game before Jagged Alliance 2 (assuming you are going to play both). Not for story reasons, there is no continuation between the games other than that some of the mercenaries are available in all of the games, with a few throwbacks in their stories to boot. Rather it is for UI/gameplay reasons, once you get used to the smoother and more developed JA2 it's hard to go back to the more primitive original JA. Also, if you are only going to play one go for JA2, it's just so much better.
Commandos is not so much a war simulation or a tactical squad game as a puzzle game using soldiers as its pieces. You control a squad of up to 6 different soldiers in the European theatre of World War II during the infancy of commando units. The commandos at your disposal are a green beret, a sniper, a marine diver, a sapper, a driver and a spy, and your missions range from blowing up a dam or a ship to freeing an informant, kidnapping an enemy commander or stealing a bomb guidance system. The missions generally sport a high level of difficulty, requiring you to map out the patrol routes of the enemy soldiers and wait for exactly the right opportunity so that you can kill them off silently and stealthily approach your objective. A straight-forward, guns blazing approach will almost always result in a quick death and a failed mission. What makes Commandos a puzzle game rather than a tactical squad game like X-Com or Jagged Alliance is that all of your commandos are highly specialised, far beyond the point of realism. For example, only one of your soldier types knows how to fire a mounted machinegun, how to drive a car or how to row a boat. The game is limited in this way specifically to force you to approach the levels in a certain way, increasing the demands on your puzzling and coordination skills but heavily reducing the realism. Some levels are flagrant about railroading you, others are more open and allow more varied approaches. This leads to high levels of frustration from time to time, sometimes to the point that the game suffers from it, but ultimately also to a great deal of satisfaction when your plan finally comes together. The expansion pack, Beyond the Call of Duty, adds a number of abilities to your soldiers, such as being able to lure guards by throwing a pack of cigarettes on the ground, knocking them out and forcing them to do your bidding at gunpoint or let your spy steal their uniform. The new features make your soldiers more versatile as you no longer need to rely solely on the green beret to lure soldiers away from their route, now any commando can throw some smokes within the enemy's line of sight and ambush them. However, the expansion also ramps up the difficulty significantly, leading to immense amounts of frustration and possibly self-harm. The bottom line is, if you want a fast-paced action game with the emphasis on gunplay then stay away from this game. If you like puzzle games, don't mind high difficulty or a "mature" war setting and are willing to suspend your disbelief about the Green Beret flunking out of the boat-rowing class in special forces school then Commandos is definitely for you. As for the technical aspects of the game, it is an isometric sprite-based game which allows the resolutions of 512*384, 640*480, 800*600 and 1024*786. The soldier sprites could have used more detail, but overall the sprites are good and the graphics have aged well. The interface can be clunky, with the hotkeys not being reconfigurable and important acts such as running not having its own hotkey. Overall it is a functional interface, including important tools such as visualising an enemy's line of sight and allowing you to split the screen into several cameras so that you can time your actions just right. The game has hotkeys for quicksaving and quickloading (and I love them so) but due to the difficulty it is important to manually save in order to maintain several save games at different stages in the mission.
