zszokowany, osłupiały

Boring: shocked, surprised, speechless, astonished, astounded

• I was astounded at how fast he could read.

Use: flabbergasted or dumbfounded

• I was flabbergasted at how fast he could read.
• flabbergasted in a song:
• dumbfounded in a song:

Bear in mind that we can use either at or by with both flabbergasted and dumbfounded. For details see the comments section below.