While researching the topic there was an opportunity to actually watch a good example of B-movie. And it was The Fly (Neumann, Kurt; 1958). The film tells a story of a scientist and his wife experiencing horrible chain of consequences because of curiosity overpowering reason. The scientist creates the most miraculous invention - the substance transporter. But instead of researching if it works as it’s supposed by gathering data from transportation experiments with animals, he examines the invention by transporting himself. The uplifting tone of the film is suddenly changed when we see the scientist half-turned into a fly.
But to get back to the conception of what is a B-movie...
As B-movie central site ( http://www.bmoviecentral.com/bmc/bmc-articles/37-bmc-articles/145-what-exactly-is-a-b-movie.html) defines: " b-movie was the second movie on a double bill. It was typically a low budget formula type film, which fell somewhere in the suspense, horror, sci-fi, western, exploitation or gangster genres"
Likewise The Fly sits in mystery, horror and sci-fi genres
Today its often to hear that B movies are cheesy sci-fi movies from the 50's. The films are filled with cheesiest dialogues and acting.
As perhaps one could notice watching The Fly, it doesn’t lack of cheesy acting, the feeling an action is "acted" (it’s not convincing or believable, you are constantly aware of the fact that this is only a film, not reality). Or reactions look over exaggerated and almost always leaves this feeling as if actor was just about few frames late to actually react.
Watching the film also I've marked , there's a feeling of "out of place" . Probably because of the difference of contexts in in which the film was created and in wich its now perceived by uc, viewers. It looks sometimes the reaction or a detail or a peace of dialogue isn't used in a good way. for example: the scene where policeman and victims brother comes to speak with an anxious murderer- the wife of the victim, she suddenly after an emotional confession of killing her husband under the press offers a cup of coffee or tea to gentlemens in a completely different emotional state ect...
To summarize the impression formed so far it looks like a B-movie's use all the conventions of ,say horror genre to supposedly create a scary film, but there's more ( cheesyness, wooden acting, campy feel) what makes it funny and amuzing.
But all works in its own way, for it creates a unique class of films with its unique set of "rules"