Best Intro Wargame

[Hiimori]

In my opinion, a good introductory hex and counter game on operational level is "Battle of the Bulge" (1991, Smithsonian Institute Series). All traditional core mechanics are in the game (movement, combat, supply, stacking) and you can start with basic rules, adding more advanced rules later. In addition, the game includes historical background information about the Battle of the Bulge, which is a nice touch for a beginner.

Another wargame which is easy to learn and hard to master is "A House Divided", introducing the point-to-point movement system / strategic level.

For a block game, I would recommend "Julius Caesar" by Columbia Games.

Last but not least, good introductory card-based wargames are "Naval Battles" and "Hell of Stalingrad" (the last game is quite easy when explained by an experienced gamer, but probably somewhat overwhelming without assistance).