Addictive gameplay, but really just a time-waster. You'll probably want those hours back.
"Mercenaries" is a reasonably solid game from the perspective of gameplay dynamics and content. Its claim to fame upon release was the fact that literally every building you see can be destroyed. This is even cooler, because the visuals and attention to detail in such demolitions are quite impressive. There are a number or unique structures which each yield their own unique wreckage.
I can also hype up how a handful of relatively simple gameplay mechanics occasionally come together to produce unique and engaging challenges.
However, the feeling I'm left with when I think about this game is disgust at the emptiness of time spent playing it. There's no "substance" to it. Games in the GTA series expose you to culture through their soundtracks and allusions to popular films. A Deus Ex game engages your imagination and expands your mind with its artfully branching storytelling. A multiplayer game allows you to build closer friendships with your buddies by teaming up and voice-chatting. Starcraft exercises your brain with its nearly limitless tactical and strategic options.
Mercenaries offers none of the above. It's "just a game," and while it's more fun than, for example, Frogger, it's a waste of time in the same degree. When I think of the several dozen hours I spent playing it, I feel like a tool for not spending that time around friends.