Many blockbuster games here. How about a huge battlefield with realistic tank battles that you can play at your own pace, and has big replayability? Acceptable learning curve, well done tank interiors, unseen scenarios (mesopotamia, africa, asia) Sandstorms, rain, aircraft and infantery included? Plus an editor for your own ideas, so you can literally create insane battles?
Try Steel Armor Blaze of Ware (demo available)
"Where's Carmack when you need him?" by cadaveca