It blows my mind = I am completely amazed I haven't heard anyone say "it blows my mind" for quite a long time but it's definitely OK. I see the adjective "mindblowing" much more commonly.

blow your mind INFORMAL If something blows your mind, you find it very exciting and unusual: There was one scene in the film that really blew my mind. surprised feeling or showing surprise because something has happened that you did not expect: We were very surprised at the result. It's not like you to behave like this, Alice - I'm surprised at you (= I feel disappointed with you)! I'm not surprised (that) he didn't keep his promise. I'm surprised to see you here. I've managed to fix your car for now, but don't be surprised if it breaks down again (= it probably will stop working again). She looked at him with a surprised expression on her face.