I could not tell you why MOO2 did not appeal to me, but it just did not. I found that the game play was ok, but only having up to 5 planets in a system kinda weak.
Of all the 4X games I have had the oppurtunity to play, BOTF was, IMHO, the best for me. Sure it was based in sorts off of MOO2, designed by the same people, but it had a lot of little details that made it worth while game that has to this day provided me with hours of game play.
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"We've made too many compromises already, too many retreats! They invade our space and we fall back -- they assimilate entire worlds and we fall back! Not again! The line must be drawn here -- this far, no further! And I will make them pay for what they've done!" -- Patric Stewart as Captain Picard
UCP/TCO Ship Yards