Yeah, puzzle games usually don't do too well, with notable exceptions like Portal, but the philosophy is really what both killed but also gave success to the series. It uses Christian symbolism in a way that could out some people off, and it really wants you to think, which some people may not want to do. If you don't participate in that aspect it's a somewhat mediocre puzzle game. With it though it's one of my favorite puzzle series.

I don't think it will very see large scale success, but I also don't think it needs to or has ever aimed for that. It wants to do something and do it well. It wants to talk about philosophy with people actually interested in philosophy. If that isn't for you then it's going to leave you behind and that should be OK. Not every title needs to reach for mass appeal.

Also, if anyone's wondering if you should play the first or just go to the second, it's fine to start with 2, but I think 1 is the better game. The graphics are worse obviously, but I think it's a better package. 2 doesn't follow the same character and there's not much story from 1 you need to know for 2, but 2 does use the mechanics for 1 and adds to it, so 1 may feel worse after. 1 takes the more limited mechanics further I think though. I never struggled with 2, even after 100%ing it, but 1 is more challenging, especially with the DLC which takes all the mechanics to their furthest reaches.