Reasonable

Generally it would suggest good, but not great.
Do you have some more context?

After [some series of chess moves] Black should have a reasonable game. However, Black's one problem will be the Bishop on c8, which is blocked by the e6 ****.

The writer used the word loosely—too loosely, if you ask me. He simply meant that Black's position is OK, that Black will have a fair chance of success.

enoonThe writer used the word loosely—too loosely, if you ask me. He simply meant that Black's position is OK, that Black will have a fair chance of success.

means more or less good game?

Please use complete sentences. It is hard to understand you otherwise, to say no more.

It is reasonable to think that Black will have a good game, but it is not certain.

enoonPlease use complete sentences. It is hard to understand you otherwise, to say no more.It is reasonable to think that Black will have a good game, but it is not certain.

Is it because of 'should have' that you say it is reasonable to think so?

soheil1Is it because of 'should have' that you say it is reasonable to think so?

That has nothing to do with it. I was just trying to explain how the writer used "reasonable". Black cannot have a reasonable game. "Reasonable" is a wrong word there. Black can, however, have a reasonably good position.

Black should have a reasonable game.

In my experience, this is commonly said. It just means, as already explained, that Black has some chance of winning but that victory is not assured.

Clive