It's got best-in-class applications with lovely animations. The server now governs reactions to specific messages. Stickers are fun, with premium stickers having additional animations.
From a technical perspective, they occupy least space; is "fast" and have a great ecosystem of third party clients. (I use "Owlgram") that offers additional UI elements without cluttering the experience. Tabbed chats are possible now; on Windows desktop, Unigram offers a stellar experience. Threat perceptions or "privacy concerns" are not in the lexicon of ordinary users like me and I am better off without Signal or WhatsApp. WhatsApp reminds me of what Telegram was 5 years back.
I think it is time to reconsider the association of Russia with the application. Criticism is fine, but much of it directed against Telegram appears biased and coloured. I don't work for Telegram, but am a happy user. I couldn't get my folks to understand XMPP or Matrix, or even get my colleagues to switch from any other competing application. This is fine by me.
Other finely grained privacy options (ability to control who can call you or add you to groups) are critical for my needs. Yes, it could be better, but no other application offers those controls. Besides, it's easy to chat with others using "usernames" without the hassle of handing out phone numbers.
Bravo!