How bad is it? Pretty bad, even by 1970's German sex farce standards.
Should you see it? No.
This was directed by Erwin Dietrich under a pseudonym; his films always look good, if nothing else, and his collaborations with Jesus Franco are among the best work of either director. Ingrid Steeger, who had a small following, especially in Germany, spends much of the film unclothed. I had hopes for this, but it's essentially plotless and threadbare. D'Artagnan discovers that the Musketeers are just a bunch of drunks and lechers and the film suddenly ends, looking like it's missing the final reel. For an obviously minuscule budget, the costumes and sets are quite good and the one unforgivably bad gaffe is having the Musketeers ride saddles that are obviously not connected to horses in front of a screen showing the same countryside, wherever they happen to go.