From my outsider's perspective, I think he's made a good start, but that the kind of program he's installing will take a couple of years to bear its fruit. The turnaround in ODIs will obviously be quicker because frankly success in ODIs is dependent less on ability alone and more on a combination of talent and intent. Test cricket really requires the ability to produce prolonged good cricket.
As the coach, Chappell can't pull up the Indian team's socks when they don't have any. He can only work with what he has - which at the moment, with Tendulkar injured/out of form is a batting line up overdependent on Dravid, with many naturally talented players like Sehwag and Dhoni that are either out-of-form, suffering attitude problems, or simply too inexperienced to be consistent match winners in test cricket. Many of these problems might be turned around, or alternatively, long term options for replacements identified and groomed, but it will take time.
My opinion of Ganguly, and its only my opinion, was that he appeared to be an unhelpful influence on the team when it needed to be reexamining themselves and rebuilding it. Its a tough call to make, but if you aren't going to help, and your form isn't great, for the long term future you need to go, even if its painful in the short term - no individual can be bigger than the good of the team, be it a Tendulkar, a Lara, let alone a down-on-form Ganguly. I think Chappell's willingness to come in and make those very tough calls, and wear the subsequent slings and arrows, will probably be his greatest legacy to the team, along with expanding the aides and techniques the team uses. I think a biomechanist will be seen to be a great addition if it improves the fitness and availability of the team.
If the ingredients that made India one of the best two teams in the world a few years ago are no longer working, it helps noone to try and continue living in the past - best to identify what changes need to happen to make India successful again, and successful for a long time.
He's probably still adjusting himself to the different cultural nuances of the job. In Australia, coaches, particularly football coaches being combative and sometimes rude with media can be par for the course. In a situation where he's not sure the best way to act, he's probably just trying to be himself - if he's there long term he'll learn to handle things in a smoother manner, or else he'll decide its too alien to his personality and pack up and leave.