The main difference is that Tibetan Buddhists practice tantra. Tantras are esoteric texts, which means you aren't allowed to read or practice them unless you have been taught by a living guru, who was taught the tantra by their guru, going all the way back to ancient India where the Vajrayana first developed. Nowadays you can read the meditation instructions for many tantras in books or on the internet, but if you actually believe in tantric Buddhism this is a really bad thing to do. At best it's fruitless and at worst it prevents you from becoming enlightened in this lifetime and harms you. Unlike sutras, which anyone is allowed to read, you are supposed to receive instructions on tantras from a living guru in real time.

One interesting thing about Tibetan Buddhist lineages is that their meditation instructions go all the way back to ancient India. In contrast, the meditation techniques used in modern Theravada Buddhism were developed within the last few hundred years by people who studied the Pali Canon very closely.

The importance of loving kindness and compassion for others is emphasized in Tibetan Buddhism more than other schools. The aspiration to become a Buddha for the sake of others, referred to as relative bodhicitta, is the single most important thing to cultivate on the Tibetan Buddhist path. Everything that you do in Tibetan Buddhism, every meditation session or positive deed, is dedicated to the enlightenment of all beings. Some people have the idea that Tibetan Buddhism is about casting magic spells or worshiping "gods" so that they'll give you enlightenment. Actually, everything in Tibetan Buddhism is fueled by bodhicitta, and you can never succeed without it. To give an example of this I'll show you the standard refuge prayer. I guarantee you every serious Tibetan Buddhist knows this prayer or some variant by heart, because they repeat it before every meditation session:

I take refuge until I am enlightened In the Buddhas, the Dharma and the Sangha. Through the merit I create by practicing giving and the other perfections May I attain Buddhahood for the sake of all sentient beings.

If Zen Buddhism is known for being minimalist, Tibetan Buddhism is known for being steeped in the supernatural. Tibetan Buddhism acknowledges the existence of various types of supernatural beings and has teachings on how to defend your self from them, communicate with them, and help them become enlightened. It encompasses astrology, alternative medicine, magic powers, a very intricate display of the energy body with all its channels and chakras, stuff like that. These things can be found in other forms of Buddhism, but it plays a larger role in Tibetan Buddhism.

One supernatural element of Tibetan Buddhism which has made it popular world wide is its detailed explanations on what happens after death; even people who know nothing about Buddhism have heard of the "Tibetan Book of the Dead." The actual title of the tantra is Liberation Through Hearing During the Intermediate State.

TLDR: The use of tantras, the importance of a living guru, the intention to become a Buddha in order to save all beings from suffering, and heavy supernatural elements differentiate Tibetan Buddhism from most other schools.