Valve has released a video showing off Colmar, one of the two new maps due to be released as part of the Day of Defeat: Source Summer Update later today.
It highlights the Detonation gameplay in Colmar - basically you have to join forces with other units to attack in unison.
The other map in the update, Jagd, is a more advanced Detonation mission set against a time limit in an urban setting.
Spawn clip adjustments, improved hit location detection and weapon balancing will also form part of the Summer Update, which we'll tell you about when it shows up.
And unlike so much of this stuff lately, you won't be expected to pay.