Yesterday we went to Southwick Zoo in Mendon. We have been visiting this zoo for 10+ years, since the kids were little and it has certainly changed in that time. 10 years ago it was quite small, with some very sad looking animals in small, dirty cages. Over the years we have seen the zoo expand and (generally) improve, creating new, more natural habitats for the animals utilizing high walls and/or electric fencing rather than cages. The result is much more pleasing, and its now a very nice place to visit. One of the newest and, in my opinion, best things they have introduced is a skyride, a cable car ride that transports you above the park on chairs suspended from cables. It is very relaxing and you get an excellent view of the animals from above their habitats.
A few complaints about this zoo however. Too many fairground rides scattered throughout the zoo detract from the otherwise natural environment. No bubblers throughout the park forces you to buy bottled water rather than refill your own water bottle. And in general its quite an expensive day out, e.g. entrance for family of 4 nearly $70, then extra costs for everything else in the park ($5 per person for the skyride).
Overall a good day out, but you do need to be fairly fit to see everything, its a big zoo and a lot of it is on slopes making the walking quite hard-going on a hot day.