Gimmick. I hate to say it, but there is nothing about this bar that is not just a gimmick. I'm not saying that they're lying about the contents of this bar, I'm sure that they gave it some kind of Guinness beer flavouring. The problem lies in the fact that Guinness beer kind of tastes like dark chocolate, I guess. So basically, this bar just tastes like dark chocolate, kind of.
The reason I say "kind of" is because it doesn't taste like great dark chocolate, in fact I would say that this tastes like pretty low-end dark chocolate. It not only tastes like low end dark chocolate, but the texture is also that of low-end dark chocolate, and it even looks like low end dark chocolate. What I'm saying is, when all is said and done, this is nothing more than a low quality dark chocolate bar that apparently has some kind of Guinness beer flavour added, but you don't really taste it over the cheap dark chocolate.
This bar was a failure in my opinion, but it didn't have to be. There are a few things that the folks at Lir Chocolate could have done to make this bar work. The first is obvious, higher quality dark chocolate. Something that isn't so waxy that melts in your mouth would have been really nice. The second is to separate the Guinness flavour from the chocolate. Rather than have the bar "taste" like Guinness, why not use some Guinness to make some kind of filling for the center of the bar. Some kind of cocoa/beer soft chocolate filling would be great. The key being that you make the Guinness flavour the standout of the filling. I'd want the filling to be almost or entirely made of Guinness, and let it blend with the chocolate as you bite into the bar. It would be a little messier, but it wouldn't be disappointing.
This bar is Guinness in name only, it needs an update, it's just something tourists (like me) buy in Ireland because we see the words "Guinness" on the label. It could be so much more.