It's not similar to Master of Orion 2.  It is MOO2.

I'll assume that if you're reading this then you're interested enough in the genre to have played MOO2.  If not, then go and read the Gamespot review of GalCiv2 and just assume that MOO2 is GalCiv2.

All that remains is to list the differences between the two games.  Anything not on this list can be assumed to be identical, or as close as makes no difference.  Everything.  Even the colour of the default interface.

GalCiv2 adds:

• A 3D engine with more resolutions, zooming and such.
• Simpler control of your empire's macro resource strategy.
• 3 distinct weapon types (kinetic, energy, missile) and three specific defences against them (armour, shields, chaff)
• User configurable interfaces (in theory, text file manipulation is required).
• Annoyingly slow battle resolutions.
• Resources scattered through the galaxy that can be harvested by building starbases.
• More flexible political deals.  You can offer any arbitrary combination of money, ships, planets, tech or treaties in return for the same.
• Roll-your-own ship designs (but only for visual purposes, see below).
• Cheesy rip off of quotes from Star Trek and Hitchhiker's Guide.
• Pointless technologies: Galactic Guide (allows all ships to survey anomalies) is only reasearchable well after the point where every anomoly will already have been surveyed.
• An researchable technology victory.
• Political influence; colonies sometimes just convert to your empire.
• Morality, confusingly decided both by your response to occasional moral decisions, and by a researchable technology where you simply decide (regardless of how you actually act) to be good/neutral/eeeevil.
• Crashes.

GalCiv2 removes:

• Many of the most distinctive racial traits (lithovore, cybernetic) in favour of more social traits (bravery).  Every race in GalCiv2 is essentially a Bumpy Head.
• Food freighters. Each planet's population is limited by its own food production.
• Workers and planetary-scale economics.  You build production facilities and research facilites on planets, but they are staffed based on your global empire economics sliders.  You can't have one planet dedicate itself to research while another goes heavy on production.
• Planetary defences like battlestations and ground batteries (you can build "planetary defences" but they only effect ground combat, they don't attack approaching ships).
• Super-tech weapons like stellar converters (Death Star guns).
• Different planet types (barren, irradiated, toxic, ocean world, etc).  Planets just have a rating that indicates the number of buildings that you can place.
• Planetary construction or type modification - no making planets from piles of rock, or rescuing Irradiated planets by building a planetary shield.
• Fighters.
• Weapon mods (heavy, point defence, etc) and most of the "trick" space combat technologies.  It's just plain old weapon power versus defence power.  No targetting computers, no lightning fields, no cloaks, no Cosmic Degrobulators.

I don't think I missed much.  It really is shocking how they've just cloned MOO2, right down to the UI look and feel (if not the functionality; it takes far too many clicks to get anything done).  Even the music is virtually indistinguishable.

Don't get me wrong, I like MOO2, but I've already got a copy.  If I'd paid money for GalCiv2, I'd be testy about it.