I'm talking WWII P-38 here, not the postwar alloy guns.
Weakness - watch out for guns with a loose top cover. A symptom is a wobbly rear site which does nothing for accuracy. Potentially the top cover can fly off under recoil spilling parts and springs all over the place.
The cover can be tweaked at some risk of breakage - new covers are not available - only old surplus parts.
Weakness - safety lever. I would open any WWII gun before firing and inspect the safety. They have been known to break, jam the firing pin which gives you a full auto pistol that fires without pulling the trigger. Always ALWAYS lower the hammer with your thumb when engaging the safety from full ####.
I think this one is overblown, but wartime production may have meant in some cases that the best quality materials were not used, particularly late in WWII.
Weakness - like many military pistols, its really meant to fire with FMJ ammo. If you want to shoot anything else, look elsewhere. I'm interested in the lead roundnose comment - I'd like to try those in our indoor range sometime. Brand used?
Strengths - where to start? Years ahead of its time - points excellently, great accuracy for a military pistol, good looking, loads of history.
My AC42: (Carl Walther 1942)
A bit worn but a perfect shooter. I put a Wolff Springs kit in it before firing. Recoil springs were particularly weak, extractor spring was in need of attention too (crud/rust in the extractor hole).