I'm new to the forum but i'm at mission 17 in ST:R, after having played the original Silent Threat.
The difference for me between the two are as follow:
--original silent threat didn't make sense to me at all, i just played it blindly, hoping to get to a mission that would actually give meaning to all the fighting efforts; it just felt empty and got bored with it shortly
--ST:R is a completely different story, i'm near completion now and i can't wait every night to get home to advance another mission into it, to see what else is going to happen. Suddenly it all makes sense, there is a purpose(other than staying alive of course), the story is engaging, captivating. The only thing is i found it a bit hard (played it on medium) as far as i had to lower the difficulty level to easy for one mission: the dreaded Hellfire
. In that sense is not quite fairly balanced, even a few other missions required a good bit of replays to get the bonus objectives, but hey, in the end it's all worth it. Miles better than the original.
Just my 2c