Access from multiple devices, lightweight client (hangouts is quite a resource hog on older devices), free (as in free beer for the protocol and free software for the client).
It's a beautiful app with features being added every month or so. It really feels like the people behind this care.
I've also managed to move most of my (at least the tech-savvy) friends from Messenger/SMS/WhatsApp to Telegram.
I've only ever heard people mention encryption on sites like HN etc. Do you guys think the normal IM user (vast vast majority) care in the slightest about encryption? Not trying to sound snarky.
Telegram was sold as the "secure messaging app".
Ok, did not know that. I do wonder if the majority of the users use it for that, or if they followed the early adopters that, obviously, care about that.
Telegram group chats ARE encrypted (in transport) they're just not end-to-end encrypted. Telegram themselves (with server access) could potentially read the messages.
Sharing media is very easy, especially multiple pics.