Keep in mind for this post, I've not been to DLRP since 2005 and it's before my "wealth" of experience since. So this is a "pre-enthusiast" view.
The original Space Mountain I had mixed feelings about (I've not done 'Mission 2').
I loved the build up, the music and the "trip through space" aspect. I thought it was a brilliantly put together "ride experience".
The launch I found dull, but part of the whole experience. The ride though did nothing for me. I don't understand the point of inversions on a dark ride (and the original SM was pretty dark). You can't tell the difference between inversions or high-g banking or whatever. It's just a bit odd.
I loved the reaching for the moon part where it falls short though, brilliant bit of ride...
So ride-wise, nothing much. As an experience, it was pretty good.
RnR? Really disappointed. I found it really a bit bland and totally "meh". The launch was quite good, but found it slowed down really quickly. Going into the half loop takes out the punch from the launch too quickly.
The rest of the ride I just found really dull. It really didn't do anything for me at all. There's the music (which is a nice distraction) and the light show. The ride though I found really bland and obvious. No great forces, lots of dead spots and unlike SM, the actual "experience" was rubbish (and I'm an Aerosmith fan).
The best bit of the whole ride is the way the doors slide open into the station just as a train is ready to launch - brilliant piece of timing.
So, big fat "meh" overall from me for both.