Most people don't realize this, but good grammar is very important when trying to make an argument, or simply getting an idea across. Without it, it makes getting some form of respect very hard as most people don't want to try and anolyze a statement any longer than need be.
It's true. Personally, whenever I see bad grammar consistently I read it similarly to how Harry sounds.
I love the aspect of simply traveling in the wasteland. I love the moral decisions. I love the varying degrees of conflict, from things like "Please! Help me find my dog!" to a remnant of the U.S. government that wants to kill everyone. I love the appropriately absurd mutants. There are others I don't feel like listing.
EDIT: Ha, I just realized that it was "What you love about Fallout Series discussion" and not "What you love about the Fallout Series".
Well, pretty much the same reasons as everyone else.