Brick,
Classic Hornet: Promise, 500-mile strike radius; result, way less than that, and by the time it had decent avionics (C/D) it was so heavy that the D had no bring-back.
B-1B. Initial goal, crank out 100 jets fast and cheap during the B-2 risk-reduction phase. Result: ECM nightmare, cost overruns, reliability issue.
B-2. Goal: 132 jets. Result, 21 jets due to delays and overruns, maintenance still horrific, vast price tags for any upgrades.
V-22. 22 years in development, expensive to buy and maintain, continuing engine durability issues, tiny payload for its size and cost.
A-12. Overpromised, failed dismally.
F-22. Mostly worked, except for promised low-maintenance stealth (which still seems to be a problem), less-than-expected combat radius and horrible costs for DMS and upgrades...
Most nations have not done much better...
But if only there was one nation somewhere that had been among the first two or three countries to introduce swept wing fighters, practical supersonic fighters, integrated radar/missile systems, datalinks, pulse-Doppler radar, large-screen glass cockpits, and had done it on tiny budgets... and if that country was the only one ever to field a new fighter that cost less to operate than its predecessor...