The Germans called the P-38 the "forked Tail Devil". It's climb
rate isn't really the best. The Japanese Kawasaki Ki-84 can
actually out climb the Lockheed P-38 Lightning if the pilot starts
with an altitude / speed advantage.
What the P-38 excels its that both propellers are counter-rotating
which in turn, eliminate torque effects.
It is a very popular plane among pilots because it's a plane with a
very low stall speed. (60 knots with full flaps) This in turn makes
landing extremely easy.
The P-38 is the TRUE master of the HAMMERHEAD ACM move.
Single engine planes such as the German's BF-109 and FW-190 will
tend to torque roll at low speed / vertical manuevers.
The P-38 was also the 1st plane in service to have all flushed
metal riverted skin, tricycle landing gear, turbo-charged engines,
one nose mounted cannon (AN-M1) and 4 machine guns (.50 cal
MK-2)
Its nose mounted armaments removes all gun convergence issues which
is a major problem in both the Supermarine Spitfire and Hawker
Hurricane. (Hurricanes have a factory default gun convergence of
400 yards. If the pilot fires at a target at say, 200 yards, the
bullets will simply fly right past the target plane. Pilots solved
the problem by tuning their guns. P-38s don't have convergence
which makes its guns very accurate even at long distances.
Also to add. The P-38 gained most credit when it shot down the Mitsubishi G4M "Betty" carring
Japanese Admiral Yamamoto.
There are two drawbacks to the P-38 design.
1.) It's unique size makes it an extremely big target. It's easy to spot it from a
distance.
2.) The P-38's air-frame wasn't designed to go anywhere above 250
knots / 400 mph. Many loss of the P-38 were due to over-speeding,
causing the plane's air-frame to "compress" at high speeds, which
in turn, locking up the controls. Newer models of the P-38 had
"Dive-brakes" installed to correct this problem.
I think that's about it all. Maybe someone can continue for me
here. 
