Do the grinding levels of coffee make a difference in taste?

Yes the grind of the coffee makes a huge difference. Basically what happens you when make coffee is that you are extracting the coffee oils from the beans, so the finer the ground, the more surface area has been exposed, so the stronger it is. Different methods of making coffee do require different grinds. Turkish coffee requires the beans to be powered. Espresso based drinks require it to be fairly fine.. sorta like fine sugar I guess. For drip coffee / french press I use a medium grind, and if you like peculator coffee then course grind is best. Not sure why Gevalia should be finer then Starbucks/Cariobou though. If you bought beans and got them to grind it they probably just got the grind wrong.. or you asked for a grind for a different coffee making method... Hope this helps :)