There aren't very many places for properly "grown-up" dining restaurants in JB, but Tera Thai is definitely one of them.
Tera Thai serves only Thai food, and unlike many other "Thai" restaurants, the food is pretty authentic. Beautiful, bold flavours and full of character. I've been here many times, often ordering different things just to sample the variety, and I've yet to be disappointed. My favourites are their glass noodle salad and red ruby dessert.
Location-wise, it is a little difficult to find, especially if you're not a local. However, it is set in a very quiet part of town, in a beautiful, converted old mansion with gorgeous landscaping.
A little more expensive than other "grown-up" restaurants in town, but I always enjoy a trip to Tera Thai.