How do metatables differ?

["kaishaku13" <kaishaku13@...>]

Looking at the documentation for work4, and reading
what I have here. I am confused about how metatables
differ from tag methods. I currently use tag methods
and understand how things work. Its nice and simple.

This is my first Lua implementation, and I am going
all out with userdata/tags for an OO API only, no
regular global functions.

I am wondering if I should make the switch over to
work4 before continuing too much on my project. I
can do so now without too much fuss I think.

So can someone explain to me how metatables actually
differ from tag methods? I'm not seeing it, I see
metatables as tag methods with some changes to the
method names, or additions like "call".
("call" could actually be useful to me, but not too important)