Free FPS, lots of fun - Combat Arms - You can buy stuff ingame, but not the sort of stuff that confers any advantages to the owners, just convenience & cosmetic stuff. No adware, just some "slurpee" banners on your way in.
For a seriously realistic (not free) wargame, check out Playnet's World War II online - a.k.a. Battleground Europe. Many infantry types, planes, tanks, artillery, naval pieces all set in early WWII, Western Europe theater. BY FAR - the largest MMPORG map around, dwarfing SWG with no zones.