When did you attempt to complete it?
Having very recently (two months ago) completed the Deus Ex: Human Revolution - Director's Cut on Steam I can be certain that I didn't encounter any such AI issues. It all worked as intended and this included a stealth no kill run (apart from the bosses).
I only played it a few days after release. Haven't touched it since because of the terrible AI. I haven't heard about any patches that fix the AI issues so I haven't bothered going back. I'd frequently encounter things like going into the sewer (while behind chased) and they'd know exactly where I was the entire time. They'd shout stuff like "he's over there" (I can't remember exactly what they said) despite being on the road above the sewer and I'm sneaking around, they just follow you through the floor and wait for you to come up another exit. Similar thing happened inside buildings that had multiple floors. Completely ruins the experience.
Regarding the actual sale the only thing I've bought is Payday 2 for £5. I've got a huge backlog of games and already own almost all the games that have interested me and been on sale. However I made the sale badge and crafting the badge also gave me "Rubedo Plated Viper Skins" for Warframe (http://steamcommunity.com/market/listings/230410/RUBEDO PLATED VIPER SKINS) and I sold them for £16, so I've actually made some money during the sale
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