"You've all been selected for this mission because you each have a special skill. Professor Hawking, John Leslie, Phil Neville, the Wu-Tang Clan, Usher, the Sugar Puffs Monster and Daniel Day-Lewis! Welcome to Operation MindFuck!"
They cant really be compared as they are different games. Nexus isnt a build up a fleet type game. You have a fleet of ships which you must use to do a set of objectives. The ships are chosen for the mission, but you choose the equipment and fighter/commando attachments.
Basically a colony ship was sent through a Wormhole in orbit of Mars. But never heard from again, and the wormhole dissapeared, presumed unstable. You discover, that it was stable and the colonists have set up a new empire, much greater than the corporations that earth have. The Noah's ark colonists (from the colony ship) had help from a hyper advanced pacifist race called the Vardrags. Who used the earthers as soldiers against the Gorg, in turn for advanced tech. I wont reveal more but i'll give you a basic set of race descriptions.
Non-Noah earth: Basic tech, several megacorps and the ISA (international space agency or something like that). Chemical rocket ships, no shielding, spinning artificial gravety suits. very Babylon-5-esque.
Noah: advanced, functional designs. The colonists from The Noah's Ark. Tech derived from the Vardrags.
Vardrags: Isolationist, pacifist. highly advanced. Travel in huge, heavily armed cityships.
Gorg: aggressive and honour bound, parallel in tech to Noah colonies.
Raptors: Genetically engineered killers created by the Vardrags.
Ghosts: Elusive, enigmatic beings that help the Noah colony by supplying information. High stealth tech. Not as capable offensively.
Well...you are technically old earth tech, first commanding the starship Stiletto...but then you begin working for the Noah colony when Sol is sort of invaded.