I guess I will be the dissenter here. I think it depends on what part of the thrill ride scares you most. I am not a roller coaster person, as I hate straight down drops. On top of that I really have a dislike of water rides. I think it was probably due to the fact I was talked onto a water flume ride at Knots Berry Farm at a young age and hated it. To put it in perspective, I love the Pirates of the Carribean but would love it even more without the drops because I just don't like them. They are mild and there for a purpose (at least in
Disneyland), but I could easily live without them
That said, I LOVE Big Thunder Mountain, mostly because the bigger drops are curved and not straight down and the others are more like a bumped up hill. I don't mind going fast around corners, just can't do drops (or go upside down). I've ridden on Matterhorn and liked that, as well as Space Mountain, but Space Mountain is about as extreme as I will go.
I avoided Splash Mountain for years and years, and finally I decided, hey, I will go on it (at Disney World) and try it. I absolutely hated it and couldn't wait for it to be over. The theming was good, I think. I don't remember it. I think part of it was I worked myself up over it as it was a "flume ride". However when I got the bottom of the last drop I was so worked up, I lost my breath and everything. I know, big baby I guess. I really thought I was going to hyperventilate or something. Of course the friends who were with me were laughing and not helping either...
So, I guess it would depend on what your fear is and if you think you can conquer it. I, personally, will never go on Splash Mountain again. But you may have a different experience and love it. You have to decide if it looks like something you think you may like try. If you do go on it, you will survive it and then you can decide if you like it (like Indy) or you don't want to do it again. There are certain Disney rides I know I will never go on, because I am certain I won't like them like Tower of Terror, Rock'n Roller Coaster and California Screaming to name a few. If if it looks like you "may" like it, it may be worth trying it once.