The F-35 is a pretty mixed bag, so lets review all of its charteristics. <Stealth
The F-35's stealth is pretty powerful, it can be detected by radar but at much shorter range then the F-35 can detect non stealthy missiles and aircraft, this allows it to fire before being seen. <Sensors, Situational Awareness, and Communications
The F-35 has very good sensors and radar, which it can pick up other planes and missiles from long ranges and it can also communicate very well with other planes and help them find targets to attack, these senors also provide very good situational awareness of what is occurring in the air and ground. The F-35 also has good tacking of ground objects such as Tanks and SAMs. <Electronic Warfare
Arguably the category that the F-35 excels best in, it can use flares, chaff, jamming, etc very well. Thier are plans for it to begin using anti-radiation missiles as well. Its electronic warfare capabilities are similar to the dedicated electronic warfare aircraft, the E-18. <Armaments
The F-35 can only carry internal weapons without sacrificing stealth, this heavily limits its armaments and what it can carry <Speed
The F-35 can't fly at or above Mach 2, oftentimes F-35 fighter groups don't train at supersonic speeds.
Keep in mind that the USAAF uses an air doctrine that minimizes its weakness and maximizes its strength, The F-35, for a stealth plane, has relatively lower maintenance and is easier to produce then other stealth planes. It is a good plane, is it better then the J-20 or Su-57, probably not, but it doesn't have to be because it is produced in much larger numbers then both those planes combined. Also another mystery factor is training and doctrine, we don't know if China and Russia have better doctrine and training then the US or if they are worse at these categories. If your training and doctrine for an advanced weapons is bad, then that weapon is useless.