Which games in this series are a must have?

Please let me know if there are bugs, errors or AI issues in said games while running on modern systems.

so 2140 has AI issues. what about 2160. it is a great game?

I think the review section would tell you the tale better.

My quick review:

2140: Starts fun, but the campaign missions feels repetitive and often tiresome to complete. Plus the AI always get a free army to attack you when it wants to, make mid-late game frustrating.

2150: The only game I really feel like a commander in a future war. Overall pretty immersive. The difficulty is moderate, the introduction of unit customization is interesting.

2160: Gameplay wise pretty solid, although in some area they add too many things without good balancing (not that previous games have great balancing though). Campaign story feels like B-class movies, instead of a real war, but is fun to play.