I must agree with the previous post on one thing, both SCF 1 and SCF3 do have have more features than OP, however the biggest drawback of SFC3, in my opinion is the number of playable races (4), while OP has 8, plus 8 playable pirate cartels. That particular feature makes the game attractive since you can play as a pirate as well as as a member of a star empire. There was actually supposed to be 9 playable races in SFC3, but unforunately that never happened for a variety of reasons. Though to be fair i must add that there is a way to create a 9 race map in SFC3, instructions on how to do it can be found at the Starfleet Universe website, i cant post a link since its been a while since i downloaded that stuff and cant remember exactly where to look for it. Plus various mods for SFC3 game add more races as well, but the same is true for OP.
The other thing you may want to think about before choosing which game to buy is its price. SFC3 goes for up to $100 on ebay, if not more. On amazon it starts from about $70. OP on the other hand can be acquired for much less, i just seen a brand new copyon amazon, several in fact, starting from just $12, that is a very good price for a brand new game this old, obviously as years go by there is fewer and fewer copies left, so if you are a gamer, and a fan of trek games in particular, i would get both games now! Give yourself a treat for the holidays. But, on the other hand, if money is tight, go with OP.
Well, i hope this helps.
GermzSlap