As a vegetarian I would give them 3 stars for their "solid-not-special" menu.
But as for the vegan part - they just offer it without knowing how to make it. Not even 1 star for that part.
On two occasions my wife complaint about her food - not tasty, no spices at all - and the waiter, in a ridiculous over the top Italian accent (some Germans seem to love that) told her in all earnest: "it's not tasty, signora? It's because it's vegan, you know!"
No excuse, no refund - two times in a row.
Updated from previous review on Saturday May 23, 2015
Cons: too many seats near the entrance door - draft, the staff doesn't engage with the needs of the cos, cook doesn't really know to cook vegan