1.) Interstellar Assembly
18.2 years build time. +50 opinion modifier with anyone in the galaxy and +100% immigration pull. If pop growth is the single most important thing in every play-through of 2.2, then this megastructure is extremely valuable and realistic to see the light before the end of the game.
2.) Strategic Command Center
24.5 years build time. This thing gives you +15% Sublight speed, naval capacity, more starbases, and defense platforms. A must have for anyone that’s playing on the largest galaxy setting.
3.) Matter Decompressor
31 year build time. Gives 1k minerals per month when completed. Basically the Mineral Version of a dyson sphere. Better than a dyson sphere solely on the fact that you’ll finish this thing quicker. And unlike energy, Minerals are a rarer resource that become more important the less habitable planets your Empire ends up with.
3a.) Mega Art Installation
18.2 build time. +300 monthly unity and +15% amenities for all planets. A realistic choice for empires having trouble keeping their pops(or themselves) happy, or looking to demolish an amenity building or two. No planet can become specialized with unity, so a plus 300 monthly modifier can mean a lot to empires without that many planets to use throughout the game.
[-4-].) Science Nexus
24.5 years build time. [300/330] research across the board(depending on if you get the brain event) [and you get up to +15% research speed]. You can easily beat this with a single planet specialized for science production, but the research speed makes this thing worth it.
5.) Sentry Array
25 year build time, gives full sensory data on the galaxy. Eh. It’s okay for those who really need to know what your opponents are doing.
[-6-].) Dyson Sphere
55 year build time. 1k monthly energy when completed. Despite the build time, 1k energy is still amazing.
5 year build time. Like, what? Six to eight max districts and no ability to build housing, science, or amenity buildings-unlike planets. Mainly only useful to be specialized as fortress, foundry, strategic resource, consumer good, or even food production habitats. Better than ring worlds, if only because you can rush to get them out before 2300.
7.) Ring Worlds
58.33 years to complete. 50 possible housing, farming, or generator districts [per each one of the four sections], can build normal buildings, but can not build any mineral districts. Realistically these things are mainly worth it to help you fully switch all your normal planets to mining worlds. Not being able to build mining districts really decapitates the value of ring worlds. ‘course, who’s to say you can’t just go all into energy production and spend all of it on monthly mineral trades on the market?
(Build time is without taking into consideration Mega Engineering, the Living Metal edict, and the Mega Structure unity ambition.)
Original Link – Continuation of discussion