Expand upon the dictionary audios, if not already - I really like the audio features that renshuu provides, it's much simpler than duolingo or any other website, I can just click on the audio button right next to the word to hear the sound
We are slowly expanding things (although right now, we're focusing on expanding our sentence audio), but it takes a lot of work to get quality audio in there. We've already added over 1,000 sentences in the last month, and have about 1,500 more to be added before the month's end :)
But we are a two-person company, and with our freemium model, we have to be picky with how we use our time and financial resources :)