A damp squib
Definition 1 of 1
Pro Tip 1/3British Origin
The phrase is more common in British English than American English, where it might be less recognized. 
I mentioned the event was a damp squib, but my American friend didn't understand the expression.
Pro Tip 2/3Use in Disappointment
Use when describing events, projects, or plans that are less exciting or successful than expected. 
The launch party was a damp squib because hardly anyone showed up.
Pro Tip 3/3Metaphorical Use
It's often used metaphorically and not taken literally, referring to the 'fizzle out' aspect of an expectation. 
The much-awaited sequel to the game was a damp squib compared to the original.