I have many of the games in the Squad Battles series and find pbm particularly addictive. I'd suggest picking up the titles that interest you - you can't go wrong.
They all play and feel a little different from each other (reflective of the conflict and
technologies they depict).
Tour of Duty can feel like a hard slog through the jungles - particularly when you're on foot (which is most of the time) and traversing uphill through jungle/wooded terrain - but then again that's kinda what it was like apparently.
I like that I can learn about conflicts that are not often depicted at this scale: First World War, Korean War, Soviet Afghan War, etc.
If you're looking for graphics enhancements for Tour of Duty, Vietnam, Modern War, Pacific War, etc, feel free to check out my blog where I host several squad battle mods that I am actively working on (Will also have my first Ancient Warfare mods soon).