Temerlyth the Undying takes a stat block, that of an elven lich with fifteen class levels, and develops it into twelve pages of information. It supplies two and a half pages of stats and abilities, almost all of which are conveniently linked to the d20pfsrd. In addition, it has half a page for his motives, half a page devoted to his appearance, and several pages for his background, personality, resources, lair, network, and even a paragraph on his morale and and preferred advancement options. There are three plot hooks provided that allow Temerlyth to be dropped into almost any campaign, given a bit of work to tweak him for the DM's world. The last couple pages are devoted to Temerlyth's companions: his kids, his adulterous wife, and her human lover. The four of them are fully statted out and ready to go for any encounter. On top of that, a new 5th-level spell, Silvermist, is included as an early find from Temerlyth's lair.
Temerlyth is well-constructed, imaginative, and was honestly fun to read. I think that, with the background information provided, Temerlyth could keep a party busy for several sessions, depending on what plot hook you use. The only part that I didn't like, and the one thing that surprised me, was the lack of even a mention of Temerlyth's phylactery. Even his Rejuvenation ability, which should mention that the phylactery rebuilds the lich's body at the least, merely states that liches can return after a few days. While it's easy to make up--a small silver box inlaid with not only the standard magical phrases but also with anti-werewolf spells--it makes the lich feel slightly incomplete. Hopefully, the adventure promised on the back cover will include this information.
[4 of 5 Stars!]