I have not seen the Tamil Version, I have seen Memento, but I liked Aamir's Ghajini. It is a full blown masala movie with a proper South Indian touch.
Especially the song, "Behka re Behka" looks like a Vijay/Surya (the Tamil actors) song. The colors and the junior artistes and all that. And story is like a gripping Puneeth Rajkumar movie. All elements of action , romance, flashbacks, revenge and after a loonnng time in a Bollywood movie, a villain who is black character (no grey shades at all!!!). The villain reminds me of the 80s and the 90s villain- travelling in an ambassador and wearing white kurta and pyjama and really huge guy with gold chains and going around with 10 guys behind. Something like Spot Naga. Aamir shouts and snarls like a proper South Indian hero before going to beat up the baddies.
Anyway I think this will be a 50 day or a 100 day movie and rake in the moolah at least in India.