Operation Citadel is a turn-based WWII themed 2D game in which you can play against a friend, the AI or follow one of the campaigns. You can also use the in-game tile editor and unit editor to come up with something else if you'd like !
Hex of Steel is an incredibly deep wargame with massive amounts of options that may make veterans of the genre truly delighted. That said, the game is not particularly welcoming to new players, lacking tutorial modes and only providing external Steam guides and videos.