I’m not too familiar with Leigh.
“Meantime” was cinematic in my book because the mood of it and the authenticity of the environment was enough to feel transported to a netherworld. “Naked” attempts this transportation, but fails slightly. Mostly because our hero is without support. So the focus is on him, which overshadows the world around. In fact, he is creator of that world (the world of the movie). But he’s no artist. Simply over-eloquent. So the world is flat, dull, and texture-less. It’s words. In succesful structures, the words echo and bounce around the environment with enough power to dynamically extend the dimensions of the experience. But not here. No world, no surface, no bounce.
The problem is, that we’re made of the world, the world’s not made of us. Character studies often miss that notion which is so obvious to cinema: the meaning is in the eye. Cassavetes succeeded because his eye was on the emotional texture of the characters (actors), and it was his soul watching, thus us watching his soul. Leigh is into the abstractions of characterization. Makes for some good acting exercises, but not interesting, not cinema. Reading a Henry James novel is more engaging than writing an essay about it.
But with that said, Thewlis is a good sport. But please look for Bremner. His entire body, posture, and mannerisms are much more cinematic than our hero here (Thewlis). Turturro, Penn and Del Toro have all borrowed from him. Hoffman, DiCaprio, and all other down-syndrome actors.