We like Olive Garden OK, but among the chain links, we much prefer Macaroni Grill. Olive Garden's Alfredo is cream-based and rather thin.
The REAL stuff (which Alfredo's should have, since it's their namesake's) is basically two ingredients - pure butter and parmesian cheese. It's heated until the cheese melts and is made into into a thick sauce, tossed with the pasta, and topped with more parm.
Lord, it's rich. Good, too, but a little goes a long, long way. DW and DD can't finish an entree sized portion. It will sit heavy in your tummy for the rest of the day. I think it's better suited to an appetizer portion, which they offer at dinner.
Alfredo's seems to have improved lately; our last visit was the best ever.