There are two things about the P-38 that give me trouble after every lengthy gap of not flying it: it's handling at speed, and the concentrated gunfire.
Until I get used to the P-38 again, I can end up going too far into compressibility and smashing into the ground, or just doing some dive or split s, getting a lot of speed, and not being able to pull out at the bottom due to reduced elevator response, in situations where I'm timing a pull out that would work in a plane such as a P-47 or F4U. I have to be aware of my speed a lot more in the P-38.
The concentrated gunfire is good for lethality, but my aim is not that great until I get used to it, and get used to aiming more carefully than I do in a plane with wing-mounted guns.
I especially like the P-38 because it saw service pretty early on (for US planes, that is).
I wish the P-38G didn't have the darkened glass on the gunsight -- it was actually optional and meant only during times of bright sunlight (like sunglasses). I would then fly the P-38G a lot.