A gorgeous movie and a worthy addition to the Terminator mythology. It does much to de-emphasize T3 and bring the franchise back up toward the standard set by the first two movies.
Cons: The Arnold cameo was forced and pointless. The ending was flawed. There are some unanswered questions. Insufficient character development.
Pros: The post J-Day world was portrayed perfectly- dark, gritty, and scary. The Skynet hardware was gorgeous. We got our first real look at a world only glimpsed in the other movies. T:S created a great precursor to the future scenes we've seen in the other movies, and had many, many subtle (and not-so-subtle) tie-ins to the other movies. McG and crew clearly care about the franchise, and it showed.