There were maps for DoD that weren't "bought" and just stayed as third party ones, you could find them regularly to play though back when the game was bigger but people slowly drifted back to the same ol Avalanche/Flash/Donner/Kalt/etc. rotation. Half the official maps were even hard to find regularly in 2005-2006ish when DoD:S came out. There were tons of maps with bridges and rivers so it's not that specific.
I played gobs of the DoD (from alphas forward), but I've mostly stayed on DoD:S for any DoD fix for years now because I sorta prefer the class diversity and Support in particular. There are plenty of quirks and changes compared to DoD, for most of the time the rifles were not as effective as in the old game, now they're closer but it still doesn't play the same. If you want a DoD-like experience that has some changes and better graphics for $2.50, I'd say go ahead. The only real balance issues I've seen is that you have to know the optimal range of your class and the maps to best put yourself in place for encounters. (And the Axis/Allies Rocket sidearm will always be off completely in my opinion.)
Although things have slowed down quite a bit since TF2 and L4D have came out. It's harder than it used to be to find good rotations with people who can play in organized and rational manners. Hopefully Valve can convince some more people in for the next couple weeks, looking at the Steam Stats looks like a lot more people are at least giving it a try from the sale.
What do they want? UbiDRM?
