S1 used to be a Great Place to Work!! Unlikely that ACI will keep it up...
Pros
S1 Pune (International PSO) was an awesome place to work - one of best talents and places that I've worked for so far. I was given complete freedom and flexibility at work, good compensation and some very challenging work. Great colleagues, especially from Europe, a good sense of being one-global-unit and a fun, party culture!
Cons
Working with Asia Pacific Management was a sad experience - it all changed in 2010-2011. I don't know how the management based in Singapore got where they were but they clearly lacked work experience and seemed to have no idea how to run large units within truly international companies. They were all expats for Singapore - they introduced an element of racism and ugly management in a great workplace such as S1 - and sure enough, they lost all great talent in the process. I quit S1 because of similar reasons as well, APAC being my last engagement before leaving - if the APAC Management would have been talented like the rest of the S1 world, I would have stayed back. Stay away from S1 if being hired for any of the APAC Professional Services engagements.