sorry i'm a bit slow at getting back to you -
to answer your question, i was brought up in the christian faith, but it was fairly open, and not really any particular denomination. although both my parents were themselves raised catholic originally, but that's another story. to be honest, having only attended two meetings, it's hard to make a fair comparison. Although Buddhism is obviously an ancient religion, SGI is a 20th Century organisation and centres around the teachings of 13th century buddhist scholar Nichiren Daishonin. Rather than having a sermon at meetings, members tend to chant for a set time and then discuss a set topic, in a more democratic manner, for example 'how Buddhism helps you in your daily life'. So i suppose depending on your view that could be an advantage over one of the 'big 3' religions where it's a lot more structured, or not.
I found that as with all religions, you are expected to make a leap of faith, namely that chanting 'nam-myoho-renge-kyo' morning and evening, along with some other set chants, you will become a better person, and live a better life. I definitely found it hard to make that leap, personally, but i know my friends who are in the faith truly believe it does help them in big, life- changing ways, so there must be some truth in it.
Right now, i'm feeling drawn back to my christian roots, perhaps because i find the idea of a creator God rings too true with me for me to be a Buddhist. Perhaps that's the main difference, that you don't have to believe in God to be a Buddhist, but in the innate life force which runs through everything, iyswim...?
also, i felt that although i was leant quite a few books on the subject to read up on, there were certain questions you weren't supposed to ask, esp to do with their leader, whose name escapes me at present, and also, unlike with the abrahimist religions, i didn't feel there was an awful i could really get my teeth into, literature-wise.