The Pentagon just released a report on Monday detailing the existing issues with the F-35 program and it doesn't look very good. One of the major problems seems to be the software. For some reason, each update of the software hasn't contained any bug fixes to resolve any issues with the software.
A series of bugs on the USMC's version (F-35B) suffers from are found "in fusion, electronic warfare, and weapons employment result in ambiguous threat displays, limited ability to respond to threats, and a requirement for off-board sources to provide accurate coordinates for precision attack."
The bugs have also caused the Integrated Exceedance Management System, which figures out whether or not the F-35 exceeded limitations during flight, had failed to function properly.
The ejection system also has issues and seems to be rather dangerous for the pilot if he has to hit the silk. "Recent discoveries that require design changes, modifications, and regression testing include the ejection seat for safe separation, wing fuel tank over-pressurization, and the life-limitations of the F-35B bulkhead. For these specific reasons and others, further program delays are likely."
To fire its A2A missiles, the F-35A has to slow down in order to open its weapon bay doors.
For the F-35A, the airspeed at which the weapons bay doors can be open in flight (550 knots or 1.2 Mach) is less than the maximum aircraft speed allowable (700 knots or 1.6 Mach). Such a restriction will limit tactics to employment of weapons at lower speeds and may create advantages for threat aircraft being pursued by the F-35A.
It has the same problem with using counter-measures.
For the F-35A, the airspeed at which countermeasures can be used is also less than the maximum speed allowable, again restricting tactical options in scenarios where F-35A pilots are conducting defensive maneuvers.
It's a shame we keep throwing money into this money pit.
FY15 DOD PROGRAMS - F-35 Joint Strike Fighter (JSF)