Usually the font face itself is fine, but the devil is in the quality of the hinting, and how well the small sizes in low DPIs will look. That, and the "fancier" (and by no means superfluous) ligatures, etc.
Professional commercial fonts do take high pains to get these right as a rule. The "free" ones you find scattered all over the web only do very rarely, AFAIK (which *does* mean the font deserves the low quality moniker, it will look awful at low DPIs and small sizes). IMHO, that stereotype is also attributed to the open fonts, be it deserved or not.