GC2 is a newer game and with the expansion it becomes more complicated than MoO2, but lots of folks fell in love with GC2 because they loved MoO2 and MoO3 was a big disappointment.
I suggest trying demos of each and start with the one you find more fun and/or easier to learn: https://www.galciv2.com/Downloads.aspx and http://download.cnet.com/Master-of-Orion/3000-7564_4-10247352.html?tag=all-titles-M-2
