I stayed one night at the Grand Central back in February, shortly after the hotel opened. Physically, it's a nice property, with all of the things one would expect from a new hotel....high-speed internet, electrical sockets which take all kinds of plugs, modern bath fittings, etc. The location is indeed central but this has the dual-edged sword effect of not being really close to anything. About 30 minutes from the airport and probably 20-30 from the coast.
The main problems I experienced were lousy SPG treatment (typical for SPG hotels in India)...no upgrade (standard room on a middle floor), no posting of Plat amenity points, none of the expected SPG perks. I've come to expect these from the Welcomgroup chain in India, so the noticeable problem were the "new hotel" service issues. Problems with check-in, problems with room service, problems at at breakfast, etc. These will no doubt be improved with time, but were very noticeable on my visit.
My recommendation, for what it's worth, is to stay there only if your business is nearby and you want the Starpoints. If your business is downtown and you don't care about the points, try the Taj. If your business is near the airport or beyond, stay at the Grand Maratha Sheraton.