Dear NT:

You wrote:
> 1-Great novels such as “Don Quixote” and “Bleak House” can be fun to read.
> 2-Great novels, such as “Don Quixote” and “Bleak House”, can be fun to read.
>
> What is the difference between the two above sentences?

There is really no difference in meaning except that the second one means that the modifier is nonrestrictive. So the first would be saying something like “Great novels similar to DQ and BH”; in other words, picaresque novels like “Quixote” or romantic novels with social commentary like “Bleak House” are fun to read. (Personally, “Bleak House” is a wonderful book, but I am not sure I would call it “fun.”) The second one is saying “Greal novels are fun to read; DQ and BH are two examples of great novels.” The commas mean that the phrase can be omitted without changing the overall meaning. Without the commas, the phrase modifies the subject to alter the meaning.

>
> Same question as regards:
> 3-Great novels like “Don Quixote” and “Bleak House” can be fun to read.
> 4-Great novels, like “Don Quixote” and “Bleak House”, can be fun to read.
>
> In which cases are the novels mentioned merely examples of great novels and in which cases do they define a type of great novel?
>
Same as above. The commas mean the modifier is nonrestrictive, so that would fall into the “example” category. Without the commas, the phrase is describing two types of great novels.