Is Anatman the most important concept in Buddhism?
If someone can realize Anatman then is this not basically the whole teaching?


It's certainly a great step forward on the path, but it is not the whole teaching.

This is the whole teaching.

That was a joke! But seriously, there is no truly objective answer to your question. Anattā is just one slice of one of the many pies of Buddhism. As a "mark of existence" it holds equal importance alongside the other two, dukkhā and aniccā.


  If someone can realize Anatman then is this not basically the whole teaching?


What about saṃsāra, kamma, the Noble Eightfold Path, the Middle Way, the Four Immeasurables, dependent origination, emptiness, and The Three Jewels? And a bunch of other stuff?

I too crave simplicity in Buddhism, but the more you look around, the deeper and broader the teachings become. There are 43 volumes in the Pāli Canon. The teachings are vast.


  If someone can realize Anatman then is this not basically the whole teaching?


It could be your whole teaching. Buddhism is a highly individualized practice. Our paths may run parallel, or at times criss-cross, or at other times go in entirely different directions: but in the end, we can all reach our own way to the end of suffering, and each way may be truly unique.