There's much more to the game than just stealth and shooting, though. The levels aren't simple, and Gabe will frequently have to ferret out secret passages, places to climb to and hidden items. He also has to overcome traps and simple puzzles, which often require the use of specialized goggles. In addition to night-vision and infra-red (which lets you see enemies through walls), there's an invaluable setting that points out things he can interact with.
Occasionally, Gabe will even have to protect another person, meaning you'll need to give them orders and light their way through darkened areas. In return, they'll help you up to hard-to-reach places and open locked doors for you (or in the case of Lian, cover you as you run into danger).
Even after you've finished its lengthy story mode, Dark Mirror gives you plenty of reasons to keep playing. You can backtrack through stages to find all the hidden extras, which in turn unlocks bonus stages. There's also a robust multiplayer mode that features deathmatch and team deathmatch for up to eight players, as well as "Rogue Agent," a variation on tag where only the current "rogue" player can rack up points.
