I'm only three books into it, having just finished REAP THE WHIRLWIND but it was great.
When you're done with the actual novels, there is an eBook short story by Dayton Ward - Vanguard: In Tempest's Wake that sort of ties everything up. It's a good end-cap to the series
Yes, I'd highly recommend the e-book short story as well. It's sort of a coda to the series, but as Jakks noted, it's a good story that ties up any loose ends.
I'd also highly recommend the "Seekers" books that take place after Vanguard. There are 4 of those and if you liked Vanguard you'll probably like those too. I'd love to see future "Seekers" books in fact. But sadly I doubt we'll see any future books in that series. There probably just won't be enough room on the S&S schedule for non show related stories.
And it was pretty clear to me when reading Section 31: Control that Dave was paying homage to Person of Interest.
Yeah, I remember on another thread David Mack said as much. I really loved Person of Interest myself. I have to admit I found it a bit scary as well because I can see that actually being prophetic in many ways.