(Note: this is the main, original Guinness factory. Guinness is a big deal here - they practically own Dublin, despite the intense efforts of Budweiser, Coors and Heineken (and to a lesser extent Miller and others) to advertise their way into peoples' drinking glasses - efforts which have met with some success.)
I'm of two minds about the GS. If you know anything at all about beer and brewing, you're not going to learn a ton from the experience. In fact, you'll be reminded at every turn of how you just spent a fairly substantial chunk of change to participate in a huge, virtual reality infomercial for Guinness that really amounts to a "marketing re-education/brainwashing" centre; it's designed to make you feel like Guinness is the best thing ever made and that you should spend, spend, spend more money on Guinness. (Some of it is pretty subtle/artful: for example, they mention how every Guinness stout in the world contains some "special essence" produced by the Dublin factory, which is a pretty way of saying that they produce a wort extract that they ship around the world to other brewers who reconstitute it & brew the Guinness themselves under contract. Guinness says that all North American Guinness stout is brewed at St. James' Gate, Dublin - though they don't say if this means they ship actual tanks/kegs of ready-to-drink Guinness from Ireland to North America, or if uncompleted beer is somehow finished/reconstituted by a local brewer after it leaves Ireland.)
However, if you don't know much about beer and brewing, the GS is a very big, slick operation that gives you a very basic view of the brewing process, with lots of visual candy and some neat architecture. For example, it's designed around a 7-story-tall atrium shaped like a Guinness pint glass.
To be clear, this isn't a tour of the brewery/factory. Guinness is a highly secretive operation, like a Molson brewery. GS is simply a tourist attraction.
|Walking to the factory. My those are big, Molson-sized tanks!|
Reinheitsgebot. But to be fair, that's a pretty sweet deal.
|Part of the Guinness factory, as seen from the top-floor lounge|
Many brewers, distillers and others have similar marketing-based "experiences" like the Guinness Storehouse (e.g. Old Jameson Distillery in Dublin, Heineken Experience in Amsterdam). If you're new to brewing and beer and/or are willing to pay a few bucks for a nice view and a pint, the GS is for you. Otherwise, I would skip it & use the money to buy several pints at a cozy pub with some live Irish session music, then take a real (and free) brewery tour at a smaller craft brewery where you're likely to learn & see much more and get to speak with the actual brewers, all without the marketing veneer that comes with big glitzy tours like this.