As a mere 'aviation enthusiast' who sadly never got to see a Lightning fly my opinion may be dismissed by some but here goes:
For its' intended mission; namely a collision-course interceptor against Russian bombers, protecting our own V-bomber bases, it was almost peerless. It was pretty much the ultimate expression of the 'scramble to intercept' model such as that used in the Battle of Britain, rather that performing standing Combat Air Patrols as the Tornado F3 could do.
That it was a very-good fighter as well as an interceptor (where it differs from the Tornado F3) stands it in good stead, but here the argument is less compelling...
The design was very-much "of its' time", that time being the early 1950s when the P1 emerged. As others have said, it suffered greatly for lack of internal fuel; a flaw shared by many British jets including the Hunter. Other flaws include:
The intake design, which inhibited the options to upgrade the radar
The main gear retracting into the wing, meaning that under-wing drop-tanks had to be carried in a cumbersome over-wing fashion, and limited payload carrying ability
The belly-tank, making no-gear landings hazardous.
The engine configuration, while a strength in terms of low-frontal area, a weakness in terms of maintenance.
In short, a wonderful technical achievement and perhaps the pilot's aeroplane, but not perhaps as flawless as it has been revered to be.