Black has played well so far. However, it seems to me that the last move is a slight mistake and should have been:

Click Here To Show Diagram Code

[go]$$Bm21
$$ -----------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . , . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . . O . . . . . . . . . . . . O . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . . . O . . . 1 . , . O O O . , X . . |
$$ | . . O . . X . . . . . . X X . X . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ -----------------------------------------[/go]

Black is low on the lower side, so heading toward the sentre is more important here.

That doesn't encourage white to slip underneath from the group on the right?

It's unclear to me how W can do that easily. For example:

Click Here To Show Diagram Code

[go]$$Bm21
$$ -----------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . , . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . . O . . . 5 . . . . . . . . O . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . . . O . . . 1 . 4 . O O O . , X . . |
$$ | . . O . . X . . 3 2 . . X X . X . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ -----------------------------------------[/go]

The exachnage of 23 for 24 is usually crude. However, here it looks good since W becomes overconcentrated. Normally, the shape made by stones 22 and 24 is very strong. However, here W's group is too close for it be effective.

Then 25 grabs a nice point in the centre, and it should help to alleviate the impact of W's thickness.

Alternatively, W could try this:

Click Here To Show Diagram Code

[go]$$Bm21
$$ -----------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . , . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . . O . . . . . . . . . . . . O . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . . . O . . . 1 . , . O O O . , X . . |
$$ | . . O . . X . . 3 5 . . X X . X . . . |
$$ | . . . X . . . 2 4 . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ -----------------------------------------[/go]

This could well be an overplay. I don't see how W can connect or cut after B 23 here. Even if W can achieve life, it is unlikely to be a good result. B will become thick, and already has a lot of territory.

As played, B will be very low on the lower side. For example:

Click Here To Show Diagram Code

[go]$$Bm21
$$ -----------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . 8 . . 3 . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . 2 . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . . O . . . . . . . . . . . . O . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . . . O . 6 . 4 . , . O O O . , X . . |
$$ | . . O . 7 X . 5 1 . . . X X . X . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ -----------------------------------------[/go]

The forcing moves at 24 and 26 are helpful in developing a scary central moyo.