Since these games are currently on sale, I'm looking to pick one or all of them up and I was wondering which one would be considered the best of the series. How do they stack up against each other?

I've only played 2140 and 2150, but I'd definitely go with 2150. 2140 is too meh with not a whole lot of facets to it. 2150 is much deeper and more interesting.

Agree with the above about 2150, but I also never played any of the other games.
I always liked the fact that you could bring over units from the previous level.
On the other hand, 2150 is rather difficult and has an interface you have to get used too.
Still, 3 games for only $3 is a very good deal.

Earth 2140 comes before 2150 obviously but as it's an oldschool RTS it might not be everyone's cup of tea.

Story:
The main factions UCS and ED start world war 3 over ressources and territory and it ends in nuclear holocaust.

Gameplay:
Nothing I'd see as overly groundbreaking - if you played any RTS of the era you also know what to expect from Earth 2140.



Earth 2150 then picks up where 2140 left after nuclear war.

1: Escape from the Blue Planet

Story:
The story is about the race of the 3 factions to escape earth before it collides with the sun, a result of kicking earth out of orbit by severe nuclear bombing.

Gameplay:
For the campaign you select 1 of 3 factions and need to collect enough ressources to build a spacecraft and leave. Depending on how much you manage to save and not blow on building units/research the campaign can end sooner or later. The longer you wait the more charred does earth become. During this you switch between your HQ base and the mission you are on seamlessly and can transport ressources and units between the HQ and mission (as long as the latter one has a landing zone). It means you have a persistent HQ in the background while working on individual missions.


2. The Moon Project

Story:
Shows what the Lunar Corporation faction was up to paralell to the main game's story any why they went to earth to fight over ressources instead of leaving (they are normally the most technologically advanced race, living on the moon and having advanced space travel).

Gameplay:
Same as the main game but does not have switching between HQ and mission. Added a few new units and technologies.


3. The Lost Souls

Story:
Those who were left behind from ED, UCS or LC during the initial evacuation of the base game fight over the very last ressources hours before the planet is finally dying in hopes to build another spacecraft to leave.

Gameplay:
Same as Moon Project but had a few balance changes and unit adjustments.



For the story you can play them in the order of 2140, then 2150 1 to 3 but for sakes of gameplay-only I'd suggest Lost Souls right away.

Be wary of techical issues - the older the games, the more trouble you might have. Lost Souls was the only Earth 2150 of the 3 I could play out of the box without googling hours for workarounds.

If I remember correctly "The Moon Project" includet in GOG's "Earth 2150 Trilogy" was patched to the same version as "The Lost Souls" v2.1 and you can play the "Escape from the Blue Planet" campaign utilizing the Moon Project engine with this mod:

http://www.gog.com/forum/earth_series/earth_series_mod_thread/post2

I never played Lost Souls but I read that it is the most difficult of the 3 E2150 games, so I would recommend this order:

Escape from the Blue Planet (using the mentioned mod) > The Moon Project > The Lost Souls