The place where Guinness is brewed is worthwhile stop for any beer drinker, if only to check it off your bucket list. The tour is nothing special for anyone who's been on brewery tours before, though.
As others have said, the highlight of the stop is getting a pint of fresh Guinness at the bar with a great view of Dublin and the surrounding area. It would have been nice if the bar served different types of Guinness beer (exports to other countries, for instance) so you can taste something that isn't necessarily available elsewhere in Dublin.
Definitely worth stopping by if in Dublin, although this is more a museum than a brewery. You go on a self-guided tour of the many floors of the store house and learn about the history of Guinness, how it is made, and its advertising campaigns. It was very interesting. About half way through you get a small sample, then a full sized pint when you get to the gravity bar at the top. Also if you like Guinness memorabilia the gift shop has everything you could want.
I have done this tour two times. The tour itself is very "Disney" compared to other brewery tours you will take around the world. I have always had an interest with Guinness advertising being a brewerania collector and this part of the tour was the highlight for me. The best thing about the tour is the end which is the Gravity Bar. Here you get to sample probably the freshest Guinness on the planet while sitting in really cool chairs next to the glass wall overlooking the brewery and the city of Dublin. When your done at the Gravity Bar browse through the Guinness Store for all of your shopping needs. If you are a guinness drinker I would recommend visiting at least once. Don't forget to take a picture in front of one of the large black glossy Guinness gates for your scrapbook.
Of course, the Guinness Storehouse isn't the Guinness brewery -- very few industrial-sized brewers will allow the great unwashed to poke around in their machinery -- but it is housed in part of the vast and sprawling Guinness complex in St. James's Gate.
The displays are very high-concept and arty, with next-to-no information on how Guinness is actually made. Of course there's lots on the long history of the brewery and the company, with an emphasis on their iconic advertising campaigns.
The tour ends with the highlight: a visit to the Gravity Bar, offering fantastic views across the city, particularly on oh-so-rare clear days.
The attraction is overpriced and overcrowded, the exhibits aren't very informative and the beer is the same medicore nitro-kegged stout you get anywhere else. Still, if you're in Dublin and have an interest in beer you sort of have to. Call in to the Porterhouse or Bull & Castle on your way back to the city centre for a pint of Irish craft beer to get the taste of globalisation out of your mouth.
Just the history alone makes this a trip that everyone must do, sometime in their life. Walking up the alley to St. James's Gate is a soulful event.
Now, the tour itself isn't unlike virtually every tour you've taken. The best part is the underground labyrinth which houses the pipes that Guinness used to flow through and where you can see hundreds of years of spikes thrust into these pipes so employees could get some free goodness. That's a fantastic story.
The real treasure comes at the end when you get the finest pint anyone has ever seen in the world. My favorite picture in the world is still the one in which my lips are about to caress the pint and a smile moves me to near tears.