I know masterpiece is a strong word but Jagged alliance deserves it. It's one of those games that never gets old, you can always go back and have hours of fun. To me, it's the best tactical combat simulation ever.
Much in the vein of X-COM: UFO defense, Jagged alliance is a blend of tactical combat, strategy, resource management, challenge tension and fun. While in X-COM you'll mainly manage your headquarters, research and production, Jagged alliance has none of that: instead you manage guerilla mercenaries, hired with your hard-earned money to help you blow your enemy's own mercs to pieces. This offers a unique twist I can't recall in any other game. You can't just hire all the best of the best like you would in Pro evolution soccer. These men and women you'll want to hire have their personalities and connections. First you'll need a lot of money, then you'll have to gain their trust, and then again deal with their likes and dislikes, the fact that some are damn murderers who'll kill each other at night and so on.
Once in the field, they'll be like five or six against a whole army or bastards hidden in the woods, grass, swamps, barracks, on bridges, behinds boxes, just waiting to shoot your team. Your equipment is scarce and the guns react badly to the environment, frequently jamming when you need them the most. As you conquer the island sector by sector (there's like 40 sectors if I recall well), the deeper you go, the riskier it gets, and the challenge brings some cool tension while playing it.
In fact the only thing I can imagine some people won't like in this game is the high challenge. Personally I totally love it, so I love this game.