+1 votes for Braid, Eets and World of Goo. I just got Gish on Steam too, and that's very fun.

I recommend just about everything written by Jesse Venbrux (clickie). It's free.
In reverse order of suitability:
* Karoshi series (though the application of "consistent rules" is debatable :)
* Frozzd
* Pazzon
A quick note about Karoshi: the theme of the game is largely about trying to get the main character to cutely and creatively kill himself. Given that you enjoyed Blackthorne I don't think this will be a problem, but just so you know...

I don't know if these games are too casual and fall under parlour games but I had a couple hours of fun with each of them.
Play Auditorium you have to arrange flows of colours over sound pickup points using these little directional circles, to complete the level. It naturally becomes more difficult to figure out the further you progress.
http://www.playauditorium.com/
Bloxorz you just need to navigate a rectangle block through different puzzles and drop it down the hole. The problem is its on these stages suspended in space and if half your block goes over the edge it falls.
[url=]http://www.miniclip.com/games/bloxorz/en/[/url]