Not all, everything, etc. somebody’s cracked up to be
Definition 1 of 1
Pro Tip 1/3Expectation Gap
Shows a difference between what people say about something and the actual experience. 
The movie everyone raved about wasn't everything it was cracked up to be.
Pro Tip 2/3Mild Disappointment
Used to express mild disappointment, not a severe failure or fault. 
The famous burger place wasn't all it's cracked up to be, but it was still okay.
Pro Tip 3/3Casual Conversations
Best used in casual conversations rather than in formal contexts. 
I heard so much about this gadget, but it's not all it's cracked up to be.