It can also be argued (and beleived by me and most of my Pagan friends) that Pagan isn't really an umbrella term for a bunch of "denominations" or "sects," bust actually an umbrella term for a group of diverse religions that are different than the familiy of "Judeo-Christian" religions.

My practices as an Witch (ecclectic Wiccan), the practices of my friend who follows Asatru (Norse Paganism), my friends who practice REAL Native American Spirituality (still not called by any name by most Indians), my friends who practice Shinto (including the first non-ethnicly Japanese Shinto priest) all have some different rituals, traditions, terminology, songs/chants, ritual tools, philosophy, festivals/ceremonies and more. This is much more than the differences of most Christian denominations (at least the mainstream Protestant traditions).

Yes, the different Pagan religions have some fundamental ties - nature being one of the largest, but Christians have largely turned their back on living with the changes of the seasons and the ebb and flow of nature. Ther are other things like the concept of polytheism, but as the old joke goes, if you ask 10 Pagans what are their beliefs about the nature of deities, you'll get 13 answers.