Sufiism - is it a different religion or it is Islam?

Adaab. I don't know much about different sub sects and diversities of Islamic culture but it looks like the Sufi tradition is quite different. They worship on shrine, practices meditation, uses musical instrument and have monk-like Darvishes who participate in religious dance. This differs from many other sects of Islam. Now, how does Islam (The Quran and Hadiths?) sees them? Is sufiism considered to be Islam ? (As I have read that Islam is very strict about whether every commandment is obeyed ) Is sufiism totally goes with Islamic religion? or it is seen as a different religion? Update on comment: I am looking for **all** major perspectives. This includes perspectives from Sufis themselves, Sociologists and other.