The first is that it occasionally descends into being Too Damn Cute By Half. This is particularly true of the episodes directed by Patrick McGoohan, who is a genius in many ways but is also about as subtle as a slice of lemon wrapped around a large gold brick.
The second is that it's all too prone to stepping into TV reality. I mean, yeah, it's a TV show ... but some of the things on there are just plain unnecessary. You can tell they put a ton of research into the settings and murder methods etc. that appear on the show -- so why then do they turn around and do silly things like have Silencers That Go "Pyewt!"
I mean, a "silencer" is basically the same principle as the muffler on a car's exhaust, a large cylindrical baffle that captures expelled gases -- but mufflers don't make cars hum like an electric go-cart, do they?
As I understand it, the proper name for a silencer is actually a "flash suppressor," because its intended use was to hide the flash of fire out the muzzle when firing at night for commandos and the like. The fact that it makes the gun just go Pow! instead of POW! is a bonus, but it doesn't make it so quiet that somebody in the next room won't hear it. I've heard it compared to sounding like an electric staple gun instead of a firecracker. But to watch your average detective show or spy thriller, you'd think that a "silencer" magically turns a pistol into an air-dart gun.
Oh, and did I mention they put silencers on revolvers? Y'know, revolvers with those big exposed cylinders in the back that shoot hot gasses out the side at very high velocity, causing a loud BANG! that doesn't come out the muzzle?
Silly television. :)
PS: On an unrelated note, Robert Goulet has passed away. I guess we won't be needing those Emerald Nuts any more. :(