You might want to consider adding filters. We built an online MOOC directory, specifically for R courses (http://www.r-exercises.com/r-courses/), and noticed that the majority of visitors use the filters we offer. E.g. finding all courses that are free, aimed at the beginner level, or offered on a specific platform.

Interesting. I will definitely consider adding filters in the future.

Originally, I just wanted to a build minimalist search engine that just gave the bare essentials (kind of like Google?)

I like the minimalism. Filtering is great, but more valuable when you know exactly what you want. That said, a (very) few filters for the most common reasons a searcher knows that they require would probably be helpful. Maybe start with just a free/paid filter?

Another filter: language. Many people don't speak English. Maybe you can automatically detect the language and add to your list of languages as you go?

Another filter I think is very important: only courses that have video lectures.