A budget game, albeit a good one, at full price? Either way Space Siege won't elicit any significant like or dislike.
Initially, the game made a good impression with a powerful opening cinematic, and i was also impressed by its clean, stylized yet low-requirement graphics. The story, some riff about saving humanity, also seemed a relatively compelling reason for kicking some alien posterior. I also liked the fact that the game kicked off combat almost immediately, throwing you into the thick of battle between various alien foes and the last defenders of humanity.
However, as gamespot also pointed out, it would go downhill from there. I too found the control scheme to be merely servicable, but this in an age where games control intelligently, it was somewhat lacking. Sound-wise, Space Siege is also as unremarkable as they go, with a muted soundtrack and voice-acting that was either overwrought or terribly disinterested. Some attempt was made to weave in subplots, like what happened to Clara and her father (via the datapads) but none of it really adds to the atmosphere.
In my playthrough, i strove for a 100% humanity rating, so i cannot attest to the efficacy, if any, of the cybernetic parts, but i am sure that they would have little impact on the game other than the alternate endings. Furthermore, weapon upgrades did not seem to have any effect, and neither did upgrading HRV. your perpetual companion throughout the game, seem to do much for his combat efficacy nor his rather limited usefulness. When the game ended some 12-14 hours after i loaded it in, I had still felt no attachment to any of the characters in the game, only with the rather vague feeling one gets upon going through some mediocre experience.
So, in conclusion, if you are also waiting for some of the other titles to come in september, then by all means Space Siege is quite an adequate fix. But don't expect too much satisfaction from what is basically a budget title in disguise.