I cannot begin to say how nice it is to have a place in town where you can enjoy traditional German food without having to endure all the Bavarian kitsch that it usually comes with.
I've eaten here a few times and have absolutely no complaints (other than the fact that they are no longer offering a few items that look very tasty). The staff is friendly, courteous, and accommodating. As far as the food, I can personally vouch for, and heartily recommend, the Bier Bratwurst and the Wiener- and Zigeunerschnitzel (pan friend pork cutlets, the latter served with sautéed peppers and onions). The Currywurst (bratwurst served with a curry ketchup) tastes just like it did from the street vendors of Mainz when I lived there and having it again brought back memories of stumbling into the late-Imbiss for one with Pommes after being shooed out of some Kneipe at 3.00 in the morning.
And always get the strudel...it's made fresh daily and it's delicious.
As far as the decor goes, it is a little spartan at the time of this writing. But one gets the impression when eating there that it is a work in progress and they are slowly putting together the restaurant a little at a time. When they do get all the pieces in place, their liquor license comes through, and the taps installed, Cafe Berlin (already a great spot) is going to be a real neighborhood gem.
I've already got this place set aside as my World Cup 2014 home!