I think they did a good job with the typeface. I’m a fan of the flat illustration they use, but don’t know how to feel about the portrait photography–although the diversity is nice. The gay pride is a little much, given it has nothing to do with learning a language. Unless they have a course on gender pronouns.
I would imagine that gender pronouns feature in the courses for many languages. They certainly do in German, which I’m trying to learn with Duolingo at the moment.
The gay pride image may not play well in some countries, specifically parts of Africa and some states in the USA. Perhaps they don’t use that image in those areas, to avoid offending people, but I would think if you are learning a language you are already open to other cultures and other ways of thinking.