Joyful,
I've done intervals as in the program on the machine and am not a big fan. I like to control them myself. I did "rolling hills" today and was frustrated by the timing and the incline. I overrode the thing the entire time. It was just silly. I like to increase the incline every two minutes by a full percent and the decline every one minute, then I start the whole thing over. That's a "rolling hill" to me. Not five minutes at 1.0 and then another five minutes at 2.0.
For intervals I like to jog for two minutes, run for two minutes and walk for 1-2 minutes. Actually that's what I used to do. Now I like to jog for 8 minutes, run for 4 minutes increasing the speed every minute and then walk for two minutes. I mess around with it a lot. It keeps my mind active and makes the time go faster.
I just realized another reason I like this. It feels a lot like "sets" I do when lifting and I love lifting. I do maybe five "sets" of intervals and I'm done. Even though that may take an hour, it just feels like five sets. I can do anything five times.