I don't have any special experience with flashlights in general, but I do have a Surefire G2. When I ordered it, I also got the lanyard thing (I don't use it, it's uncomfortable, to me, and I just keep it in a sheath on my manpurse), an extra lamp assembly, a box of batteries, and a "spares carrier" (which is surprisingly cool; it holds six extra batteries and a spare lamp assembly).
So far, I've replaced the batteries on it twice so far (I use it almost-never-at-all, but when I use it... whoo! by God does it get the job done!). I'm considering giving my dad one for Christmas.
~GnSx