Hi Karen, welcome to the DIS, we're glad you've found us!!
Tower of Terror is a lot of fun (if you can handle the drops, that is!). The ride starts out in an elevator and first you see some special effects like the ghosts of the people who supposedly died in the original elevator accident. The room goes dark and you see lots of stars. You then go further up and see some twilight zone paraphernelia. The elevator moves forward, the doors open and then you drop over and over. Sometimes the drops are short and sometimes they are nice and long. You go up and down quite a few times and before you know it, it's over. It's absolutely one of my favorite rides!!
I haven't been on Alien Encounter in awhile so maybe someone else can describe it better for me. I do remember it being much scarier, although you don't move - you just sit in your seat the whole time. There is a show about how they captured the alien, I think, and you can see it in the tube in front of you (the seating is a great big circle with the action taking place in the middle). All of a sudden the lights go out and the alien escapes. You can hear the glass break and hear him running around. People are screaming and then you feel his hot breath on your neck. That's about all I can remember, I'm afraid it's not one of my favorites.
Have fun!