Most of these downloadable 10 Kalavinka Press PDFs are good introductions to the Mahayana:http://ifile.it/t3aqukl/MahayanaPDFs.zip
Unfortunately that file is gone. If anyone could upload it it would be a great help.
This title has been around since the 1920s, but it is free from BDK: https://www.bdkamerica.org/default.aspx?MPID=53
It presents a Japanese perspective of what constitutes the Buddha's teachings. I'm not sure if it really fits for the category of introduction since it contains many different levels of teachings without explaining the connection.
The little book does gives many levels of Dharma, thus everyone will find something inspiring.
Bhikshu Dharmamitra will, time & health permitting, give full PDFs of his translations in time.