I was really thinking about picking this one up.
Is it a keeper??
Well....
Yes and no...
Freelancer IS a LOT better.
Dark One Star has better cut scenes, and it's easier (for me) to get a start as a trader, but it's more designed with being a merc.
The variation between star systems is about moot, in otherwords, you seen one system, you've seen them all to a certain degree.
The story starts off moving more quickly (at least it seemed to me again) than Freelancer, but it's more with the cutscenes that move it forward, and how aggressively you pursue the SP storyline.
The entire way you advance character/ship wise is different than Freelancer. DSO concentrates more on how you upgrade ONE ship, and only one ship. You don't trade or buy and sell to get a better one, you already have the best ship in the galaxy to begin with...well...to a degree. The ship has the ability to become the best ship, and even then improve, which is why I say it's already the best ship. It has the ability to expand and grow due to alien technology (and any more than that would give out spoilers). In fact, thus far it seems that the ship perhaps is part of what the storyline (and also the title, which is after the ship) is all about.
The gameplay is good, and I like it over Freelancers since you can use a stick, and WAAAY over X2 (which I thought had a terrible control system...in my opinion, then again, it also has a better economic model and a whole bunch of other items better than X2).
I'm still on SP so haven't gotten around to the MP portion yet. I'll say more later, but currently if I had to compare, I'd say that relative to other games...
If Freelancer was rated by Me I'd give it around a 95-97. X2 would probably be around a 60-65, and Dark Star One thus far would probably be around a 75%.
Hence, it's iffy if it would be a keeper for you or not. I'd say download the Demo, thus far the Demo seems pretty good at representing what the entire game is like, plus, it will also tell you if you will have any bugs relative to the game running (I've been lucky thus far, only one bug, but I've heard some people complain a LOT about bugs in the game with their systems). It IS a system hog, so you'll probably want to have a good system as well (though I do run it all things maxed, so...).
I'll write more later.