well i'm a reliance user, although not from chennai. i can't comment on their local setup/support, but there are other things which i can talk about.
first of all, i experience very little downtime with the connection. unless there is some technical fault (blown card or something like that), i can safely say that downtime doesn't occur for months. their speeds are always what they promise... if you have a 1mbps plan, you will get 1mbps and nothing less. i've known indian isps to have slower than advertised speeds, so this is a plus point. for gaming, their routing to europe, south east asia and america is the best i've seen in india. pings to se asia are ~100, europe ~180, north america (east coast) ~300. the routing will be more or less the same, no matter where in the country you take the connection. and finally customer support... let me tell you how their system works. they have 1 major hub in navi mumbai called dakc (dhirubhai ambani knowledge centre)... that is the central point of the entire reliance network around the country. whenever you have a problem with your internet/phone, you make a toll free call to a call centre in dakc... the person on the other end of the line will try a few basic things to get your net working again (eg. asking you to restart modem, reset your ip etc.). if that works, good. if not, they take down a complaint and that complaint is then forwarded to your city and the local reliance setup there. after that, the local people take care of it, and that can include home visits or they just fix it down the line. in my experience, they always solve any problems i have within 24 hours. sometimes the person who takes the call is a moron, but you can't really blame them for that... if they were qualified network engineers, odds are they wouldn't be answering phones. as long as they take down your complaint, it will land up in the lap of some competent person and the problem will get solved. this should hold true for chennai as well as any other part of the country.