All of the expansions interact with the base game in really interesting ways, lots of emergent gameplay. AI War is kind of like Rogue-Likes in that regard and the expansions really enhance and boost this aspect of the game. They've all received a lot of polish and will continue to be refined if Arcen's track record is any indication of what the future of AI War holds. So they all represent great value. Arcen doesn't do anything in a "fire and forget" manner.
That said, I'm going to take a moment to plug Children of Neinzul, especially since LotS is getting a lot of spotlight. The Neinzul units add a lot to the game for me. I just love the Roaming Enclave and Preservation Warden minor factions (I haven't had the guts to add Neinzul Rocketry Corp yet, that sounds pretty intense) they add a really fun element of chaos (for both the player and the AI). And the Neinzul units are a lot of fun and interesting to use in their own right, if a little challenging because of their life-cycle. The Hybrid Hives AI Plot really makes things interesting as well. This fusion of AI and Neinzul can recolonize cleared AI planets, for instance.
It's not as expensive as the other two expansions, giving you a chance to see how the expansions work with the base game for less investment. Also, all the profits from CoN get donated to Child's Play, a really amazing charity that not only helps people but shows the world that gamers are compassionate people and not some kind of ridiculous, brofisting stereotype.
