Guinness is just a stepping stone to "big" beers OP.
Beware the path that lies ahead of you. It's an expensive hobby lol.
I don't know that I would classify Guinness as a "big" beer in today's market. It comes in at a paltry ~4.3%abv. With beers registering in the 5-7% range as the "norm" these days, Guinness falls fairly short of the "big" beer category. It also lacks the requisite mouthfeel (body), flavor, and aroma characteristics, and is fairly watery compared to more true examples of the style.
I find it debatable that the BJCP even lists them as a commercial example of a dry stout. As I don't seem to agree with them that it has maintained it's adherence to the characteristics of the style. I am sure at one time it was a fine example of a dry stout, but I think over the years they have tailored the recipe to reach a broader target market. But that is just my opinion, there are those out there a lot more knowledgeable than myself whom write the style guidelines.
BJCP 2008 Style Guidelines - Category 13