hmm...that doesn't sound like a rave review.Working with oil pastels wasn't exactly what I expected and I'm still not really sure what I think of them.
What brand were these? The colors look very rich. I am also noticing the texture of the paper - Mi-Teintes or similar, by any chance? Although this paper is really pushed as being great for pastels, I personally do NOT like it for oil pastels. I find trying to blend in all that heavy texture too labor intensive. Maybe I'm just lazy.
But a smoother paper might make them easier to handle. 
But this is how you learn about opacity in various brands. Mungyo Gallery Soft have, by and large, excellent opacity and blend well together. You might consider a small set. They're a decent size, though not square.
One thing they're particularly good for is studies; you can lay down a lot color quick and easy, and get a pretty good idea what a final piece - in whatever medium - might look like. Terri is the best for advice beyond that 
Nice job! I like the rainbow effect.This is my first attempt at oil pastels.
I kinda like OPs. They fit my style (Quick-n-Simple) rather well. I use canvas paper and canvas board for the support. Sometimes I'll use a brush and turpentine to "melt" the color into the support, especially when I don't want the white to show through. Best advice I can give is to play (errr, experiment) with them.Working with oil pastels wasn't exactly what I expected and I'm still not really sure what I think of them.

Interesting link - thanks for that, Lamar! I always enjoy seeing how others work with oil pastels. She's using Neocolor II for most of this video - the water soluble ones. Fun stuff!You might be interested in this video of Sandi Hester (thanks again, Hermes2020) reworking an oil pastel painting starting at about minute 14:20. It's a good illustration of someone using some of the favorable properties of OPs. Also interesting that she's using black paper.