kiloquarter

The biggest issue I see is the menu. Gradients with flat illustrations don't look really good, and they can confuse the reader at times. Get rid of the gradients, although they are making a comeback, menus aren't the place for them to show. Very rarely are they used in menus successfully.

your icons for each category also don't share the same visual language with each other, more info on that here:

https://webdesign.tutsplus.com/articles/guidelines-for-creating-your-own-icon-set--webdesign-569

Further, your colours in the menu are also an issue. Having each menu element with a different background colour is a bad idea because there all fighting for attention with each other that way. Instead, you want them to all have the same level of hierarchy so that the viewer themselves can choose which category they would like. Currently the design is forcing hierarchy on certain categories through the colours, and ignoring others. You don't want the design itself controlling the hierarchy of a menu, decide what's important, and if there all equally important, then create a menu that has the same colour, fonts etc for each of them. It allows each element to demand the same amount of attention from the viewer, and the structure of mobile creates a natural top-bottom flow of information that you can use to your advantage (place the most popular categories top, least popular at bottom).

Besides your menu, your typography for the app is solid, but I would also venture into pairing another font with the current one you have. This will create contrast the two, and allow the viewer to quickly differentiate between two types of information. For example, setting your body text in a sans-serif would allow the viewer to immediately understand that serif=title (Question, Answer) and sans-serif=body copy (paragraphs). Be careful with this however: Font pairing is hard to do successfully, do some research and follow proper font/pairing rules. More on that here: http://fontpair.co/

I have more, I'll be back in a bit to possible add on to this. Cheers!

Your UI and general app brand needs a bit of patching up, currently the elements are good but the aesthetic needs some work done. I'm a designer who can help with look of the app and fix some of the issues you have, Or you can find another person to help! Either way, I recommend hiring a UI designer to come look at this and fix it up. You've done some amazing work regardless, kudos