Ignore the Counter-Strike lunatics who rate this lowly because they expected the same, Day Of Defeat is MUCH more.
I've seen several reviews on Gamespot where more or less people have been expecting this to be like Counter-Strike, and then becoming dissapointed because they're too narrowminded to actually play anything else.
They can't handle the fact that it can take one bullet to kill you, they can't handle the fact that you can't jump and run and sprint all over the map popping anything that moves.
They can't handle the fact that you actually NEED to cooperate with other players.
The best mod for Half-Life is not the over-rated self-oriented Counter-Strike, the true mod is indeed Day Of Defeat.
A slow methodical game, that can become insane in way of intensity, Day of Defeat will have you relying on your team, not running around yelling "OMG KILLZ" or other such immature blabber. Most servers will have people encouraging each other to move up once a machine gunner or sniper has been downed. Players classes will benefit eachother, a good example might be a sniper covering a machine gunner as he attempts to setup his gun on a nearby sandbag.
This is NOT a game where you run around guns blazing, in fact, if you try to run around shooting your gun at all, your aim will be so inaccurate that even if you're firing at a stationary target, he'd be more likely to put one in your side, rather than you actually hitting him at all.
Whereas Counter-Strike's community has withered down to a self-centered, immature twelve year old community, Day of Defeat will have much more friendly servers, and one single player can't be the "end all, rule all" killing machine.
So now that we've got the "What it isn't" (Counter-strike) out of the way, let's start on the actual review.
I'll start with the small list of negatives. The first thing you'll notice is that DOD has a steep learning curve, it'll take you sometime to adjust into the gameplay mechanics, you'll have to learn how to cease circle strafing, and start weaving out behind obstacles, firing off a round, then going back behind an obstacle.
It's a rather difficult experience at first, but due to the community's tolerance of newbies and struggling players, you'll have understanding people who'll be willing to show you a few tricks, or give you hints on which weapons to use.
On to the good.
DOD is extremely well balanced, all the official maps are excellent, unlike the way of most games, where the official maps are rather left behind in the dust, even after years, these maps have managed to capitivate the same community that began playing them a while back. Avalanche is a sniper's paradise, Flash is a frantic continous push of the Axis moving forward, then the Allied moving forward and etc.
Northbound is intricate and large, Donner is a pretty hard to master map, where the battle-field will be balanced between snipers and SMGers.
These kinds of maps are the meat of DOD, they'll probably keep you looking out for their names as you browse the servers.
Now, about the graphics. They aren't much special, but the weapon models are excellent, same with the player models, the official maps are beautifully textured and designed, but that's about where the beauty ends. It's all sufficient though, and you probably won't have any problems.
Pretty much a great game, just don't miss out on it if you own Half-Life, skip over Counter-Strike, and devour DOD