I'm really liking this game. It's pretty well-crafted and fun. Seems to be designed with MP in mind, as turns go really fast once the tech tree is learned. It's not a 'deep' strategy game, it's more a beer-and-pretzels game one plays in one night with friends.
Approval info here http://endlessspace.wikia.com/wiki/Approval
It's like Civ4 in that if you expand too quickly your 'economy' crashes. Prioritize the 'approval' techs, just grab the very best planets at start, and your people will be ecstatic (very important to keep the Empire approval at EDIT-- Fervent, not ecstatic (if you can get the important planets individually to ecstatic that's perfect) END EDIT, lower tax rate to achieve this, even if you temporarily lost dust/turn).
There's a few other techs I prioritize:
N-Way fusion Plants to build Heavy Isotope Refineries (this is my first researched tech and first build after the 'exploit planet' build) (right side of tech tree
Efficient Shielding (destroyers) then Applied Casimir Effects (for wormhole travel and -22% expansion dissapproval) (bottom of tech tree)
Non-Baryonic Particles to build Magnetic Field Generators (big research boost early on) (right side of tech tree)
The tech tree is confusing at first, but I soon realized if I zoom in I can see the 1 or 2 things unlocked from a tech, and those things have color-coded cues (for example, the approval-enhancing ones have a pink triangle in their upper right corner, this corresponds to the colors on the Empire page (food is green, industry is orange, etc.). There's lots of 'clues' like this I eventually discovered that make the game easier to figure out, and shows how much effort they put into the UI.
All-in-all a well-crafted game that's fun, and deserves a looksee.