So I got Manhattan Project: Energy Empire recently and played it solo a couple of times over the weekend, and now I wanna talk about it.
This game is not actually an expansion, but rather a separate sister game to The Manhattan Project. It's still worker-placement, but the theme is a bit more positive (generating energy, resources, and cash, rather than bombs), and with MUCH less take-that involved.
The key mechanic here is that the worker placement involves stacks of workers. To take an action, you have to place a stack of workers higher than the tallest stack on the space (even if that stack is yours). You can deliberate leave taller stacks to make it harder, but that cost is potential for other actions. I really like the possibility of going wide or deep with your workers like this.
To make the worker stuff even more dynamic, the way you are growing these stacks is with Energy, which you have to generate by buying a variety of custom power plant dice. The dice add a nice shock of luck into the game, because you can't exactly plan for how many energy you'll have - but you can go with clean power, dirty power, or a mix. Your energy pool grows as the game goes along, opening up more possibilities with your actions (but also ramping up pollution).
The original Manhattan Project was kind of a miss for me, but the thing that keeps this fresh is the various paths to victory and the higher emphasis on engine-building.
The only negatives for me about the game are that it's a bit fiddly. Often times my turns involved taking resources from the supply, just to return them in the same turn, as part of a chain. But you can be smart about this and count the resource as you take the next action, rather than physically take it.