IDIOMS

all sizzle and no steak

(idiomatic) A thing or person which fails to measure up to its description or advanced promotion.

Example:   Her latest novel is all sizzle and no steak.
1999, "Nonprofit community increasing nervousness about Year 2000" by Gary M. Grobman. International Journal of Nonprofit and Voluntary Sector Marketing, vol 4 issue 2.
  Y2K may be the equivalent of the Kohotek comet—all sizzle and no steak.