Hidden & Dangerous 2 is a tactical fps similar to the early rainbow 6 series and just as fun. Set during WW2 you pick four SAS soldiers and equip them with whatever you desire from a huge list of weapons and equipment. This has to last them for the whole campaign (there are about 4-5). You can also take anything the enemy germans had on them when they were killed.
The planning phase is accessed during the mission rather than before it, allowing you to make alterations to your plan on the fly. Most missions take place outdoors, so sniper rifles are a very valid choice and see a lot of action. H&D 2 had some really fantastic multiplayer maps for sniping and there is still a good sized community who play it.
H&D1 is pretty old now but it can be downloaded for free at file planet, it may be a pain to get working on newer machines.
edited for clarity
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Hurlshot is absolutly right about BF2 by the way.