Full glass front doors can present a feng shui challenge for both a home and a business (especially a small business). However, this is a very general statement because the complete and accurate answer most certainly depends on many details of the building itself.
As with everything in feng shui—in genuine, accurate feng shui that really works, not in quick feng shui used as a band-aid—you have to take into consideration all the details that surround a specific issue or an area you are trying to improve, or are concerned about.
The Feng Shui of the Front Door
Being the "Mouth of Chi", the energy of and around the front door greatly influences the quality of energy that enters the house (or the business) Basically, you want a strong, powerful and balanced front door. When your space has enough potent Chi, your health and all areas of your life are benefiting from it.
Front doors are also seen as powerful protectors, on an energy level, as your front door is the main threshold between the outer world and the inner world. You can find amazing lore and various complex designs for a strong front door in all ancient cultures. We have lost quite a bit of this knowledge, but it is all there for those who want to connect with it.
About Glass Front Doors
Now, with full glass front doors, the main concern is the weakness of the door. It is basically a see-through door, where the house is left with little protection from whatever quality of energy comes in - good, bad, in-between, etc. You always want to feel empowered when you approach a front door - especially your own - which is not happening with a full glass front door.
Basically, everyone and anything can peek inside your house—not very good feng shui!
However, as I said before, there are many other details to take into consideration when assessing the feng shui of any detail, area or item. No "thing" exists by itself, but is rather connected to literally a million things around it, some visible, most invisible, but still accessible to those who can read the energy.
So, a full glass front door that has no support to connect to (or draw from), such as strong walls around it, smart exterior landscaping, powerful main entry design or—the worst case scenario—that has a full glass back door directly aligned with it—will surely be a bad feng shui front door.