UMass is a great program... I'm an MS4 here, and can't say enough good things about the program.
The residents are great (including five women currently), and are probably the biggest strength of the program. The faculty are a good mixture: a number of young and motivated surgeons, as well as some more experienced and very knowledgable senior faculty.
Traditionally UMass is an extremely strong clinical program, with most graduates logging 2200+ cases. Of note, these are not simply gruntwork statistics... OR's will rarely have more than 2 residents at a time. PGY-2s are often doing a large portion of primary joints, and doing them well, halfway through the year. The seniors, when present, are generally teaching the case (very well, I might add). It seems as if they have usually seen enough of most cases by PGY-4,5 year that they get more out of teaching than doing. However, people in central Mass are incredibly creative about finding ways to injure themselves, and high-level trauma cases, as well as many revision jonts, etc. will definitely keep the seniors busy operating on a regular basis. In terms surgical training, and based on rotations and discussions with other MS4s, I would be willing to bet the Trauma and Joint experience here are as good as any program in the nation.
The new chairman has done a great deal to promote research, and the academic side of things has benefitted. In addition to some great basic science and outcomes research, there are now clinical research projects in joints, spine, and hand/upper extremity. Didactics are strong, mostly resident run. If you are looking for faculty to lecture you on a daily basis, this probably isn't the place for you (trauma rounds each morning at the University campus is as close as you'll get).
In terms of doing an away here, I loved it. This past year we spent a week on Trauma, a week on Pedi/Spine, a week on Joints/General, and a week on Hand/Sports, so it provided a lot of diversity that helped me out during later SubI's. Call at UMass is busy, but fun... the residents balance supervision and experience very well with SubI's.
Overall, definitely an up-and-coming residency program, and a place where I would have been more than happy to train. I would encourage a rotation, and hope your experiences are as good as mine have been.