Perhaps I'm just used to it, but I find SC's UI/UX to be quite nice to use. I would be disappointed if Snapchat's UI changed to be more like Instagram's; IG's UI may be more discoverable, but it just doesn't feel as smooth.
I liked the UI of early Snapchat (2013) when there was only a recent Snaps list and a camera view and you could swipe between them. It all went downhill from there, but the biggest blow for me was the stupid thing that you have to pull down when in the camera view to get access to your contacts. I wish the "designer" that had this stupid idea would be sentenced to several years of reading all text in nothing but Comic Sans.
