I loved the first four books, and (at the time) believed the fourth "document" to be a satisfying and fitting end to the series. Nonetheless, I was pleased to hear there was to be more Izzy, trusting the skill of the author not to fall into the Evanovich-like formula trap. After reading "The Trail of the Spellmans," I could wish she had fallen in that trap. I found the fifth book unsatisfying, unpleasant, inconsistent, and heavy-handed.
That SHOULD have cured me of wanting to read "The Last Word," but like those about to witness a train wreck, I just couldn't turn my eyes away. TLW appears to close the Isabel Spellman saga once and for all. It continues some of the themes and personal story lines from TotS, introduces new professional and personal challenges to Isabel (all of which seem to overwhelm her), and serves as a bridge to the next series, evidently featuring Rae. (I see another Evanovich-type trap looming. Sigh).
TLW doesn't have the fun, snarky, and light touch of the first four Spellman novels, but (to its credit) it doesn't seem to aspire to that either. Characters are consistent with TotS, most of the plot lines are neatly tied, and if you want to keep up with the author's next series, you will probably need to read Documents* (*finger quotes -- sorry, couldn't resist) 5 and 6. If, (like me), you're not particularly interested in Rae Spellman, you might want to stop at book #4.