I was coming here to post the sale myself!
I think the discount applies to all three of his games; Armageddon Empires, Solium Infernum and Six Gun Saga, I have all three!
They are all turn based strategy games, very slow paced but really satisfying when you can see your plans come to fruition
AE and SGS are single player games whereas Solium Infernum does have a single player option but it really shines in multiplayer PBEM, scheming against one another and watching your opponents' plans fall apart is the game at its best. There's currently a free mini-expansion being tested that does kick up the aggressiveness of the AIs in single player.
If you can only afford one, get SI, if two SI and AE, unless you really like the theme I'd skip SGS. It's an interesting idea for a game but IMHO it suffers from the fighting mechanic, the poker hands are a very thematic way to simulate conflicts (in the Doomtown CCG for instance) but here they just fall flat, I can't really articulate why.
For anyone who's not heard of these games there are demos of all the games on his website, check them out!
http://www.crypticcomet.com/