Many, I really like concepts, it's more rare that the product holds up, though. I can still like it on concept alone. For example, Dishonored - the game is meh, too easy and the abilities you get just make it a walk in the park, the story itself is also meh - almost "your princess is in another castle", the characters were meh - most of them didn't really stand out at all. But I like the world, cosmology, and background are actually quite cool. I loved reading all of the books and exploring here and there for some new nuggets of information. The idea of a godless world with (essentially) Nyarlathotep being an adversary for kicks is fascinating.
Then again, sometimes concept is not enough. Here is a different example - Demon: the Fallen the tabletop RPG. Here is the concept - you play as one of the original demons - the angels that pretty much built reality and then rebelled against heaven, headed by Lucifer himself, which caused them to Fall. They, of course, lost the war and were cast into hell as punishment. What I find really cool is why they rebelled in the beginning - apparently (according t their version of the story) they wanted to help humans but God was being a douche and didn't want to mess at all. And the hell he cast them in wasn't brimstone, fire lakes, and the souls of the sinners, but instead just the black empty Abyss where the Fallen were forever cut away from humanity which they cherished. So far so good, then comes the next interesting part - well their "forever" damnation comes to a finish a bit early - the walls of hell get slightly cracked due to...erm, nukes[footnote]long story - some people tried to nuke a vampire, some ghosts nuked a city, and one guy just wanted to nuke chaos for kicks[/footnote], which enabled some of the Fallen to escape into the modern day world. Only to find it a shadow of its former self - apparently it looks way past its expiration date and God plus the rest of the angels are nowhere to be found.
So the concept - fantastic, love it. In practice, though? Well, I found the game to be too whiny and emo. One of the central stats of the Fallen is pretty much have a how much they want to cut themselves (and others). Also, they are supposed to either be wallowing in self loathing and maybe try and regain some of their former angelic heritage by being "oh it sucks to be us, and we really really did bad things, waah" or just go biblical demon on the world with the rationale "eh, I suffered, so should they". So execution - eh, could have been better.
