Taj Mahal is my favorite Pittsburgh spot for Indian. Going on a day they offer the buffet serves as a great opportunity to try all kinds of dishes without committing to a full entree. The food is delicious and, while I'm not an expert, the recipes seem very authentic. Their chicken tikka masala is my favorite and, of course, you have to have some naan - it's worth trying the naan basket which offers several varieties.
I would definitely give Taj Mahal five stars based on the quality and taste of their food. However, I have had minor issues in the past with their basic customer service. They offer online ordering which is a nice convenience, but I have gone to pick up only to find they hadn't started my order or that my order would take significantly longer than I was told (one time waiting an additional 25 minutes in the restaurant). There have also been issues dining in - we once had a large party and there was a lot of confusion over paying the bills. I would not mention these if they were one-time issues, but these things seem to keep happening.
Honestly, these issues haven't stopped me from returning frequently to Taj Mahal. I'd like to see improvements with their customer service, but there is likely no incentive for them to improve since they are always very busy with lots of patrons. I'm not trying to knock them down; like I said, the food is wonderful. Definitely check them out for some fantastic tastes of India, but be aware you may hit a few bumps in your dining experience on the service side of things.