Is it worth buying Batman arkham city and origins @75% off?

arkham city is pretty good. still installing origins so i really can't tell about that.

Yup, definitely.

If you want to play them NOW, you should buy them. I'm waiting for another price drop, maybe they will bring the complete edition (of Arkham Origins) to Steam.

NO.
Get them here instead: clicky
(~5.64 USD for Batman games minus DLC)

I guess just a week ago the Batman trilogy was sold at Bundle Stars for around 4.15 Euros. And 75% Steam Sale has been going on since the fall sale. I haven't played Origins, but even Arkham City alone is worth that price.

If you're interested, real shame you missed the Bundlestars deal that had Asylum, City and Origins with all DLC for about $10. But yes, I'd say they're worth it.
If you need to choose though, I'd pick the City GOTY, and wait until a complete edition of Origins goes on sale for similar price. (Probably early next year)

actually i don't have a credit card so buying from anywhere else is not an option for me :)