I actually rode (and loved) RnR before Space/Splash/Big Thunder Mts.
I feel safe with a shoulder restraint -- I don't care how fast it goes or if it goes upside down, as long as I don't have to fear falling OUT

Basically you're going so fast that you're immediately pressed back into your seat (have you done Mission space?) and flying through the air on a VERY smooth track until you stop. If you enjoy speed, the roller coaster aspects shouldn't trouble you too much. It's definitely an adrenaline rush, but once you've done it it's no longer scary. Tower of Terror remains scary for me each trip -- but I still do it!
So a couple of years ago I psyched myself into doing Space Mountain. Found it jerky and uncomfortable but nothing to have scared myself over for years. Basically it's like Primevil Whirl without the whirl, if you know what I mean -- nothing drastic, just sudden turns. But it's semi-dark.
The last two trips I TRIED to psych myself up to do Splash Mtn. (Big Thunder always seemed to be closed). Stood there watching that drop, seeing the cars with just about no handles to speak of to hang onto/hold me in... and I couldn't.
This time I forced myself... and it was nothing! So I tried BTMM and that was nothing! So I ran over and did Space Mountain just to say I'd finally conquered my fear and done all three (and on the same day, yet!) and found it was really mild.
Maybe next trip I'll do EE, and then there won't be anything I can't do
