I love three of the archetypes from the book:
1. The Counter-Summoner, a Summoner archetype that trades the Summon Monster ability for the ability to counter Conjuration spells as an immediate action. While I don't think that will come up often, it is thematically appropriate and requires much less bookkeeping than the ability it replaces.
2. The Elementalist, a druid who replaces his animal companion with the ability to summon and switch between four elemental eidolons (one for each element). None of the eidolons have access to evolutions, so at high levels, they might struggle to contribute in combat. However, because they each have their own skill points and feats, they can act as a toolbox. Right now, I have a knowledge monkey (fire), a rogue (air), a bodyguard (earth), and a tripper (water).
3. The Monster Tactician, an Inquisitor that trades most of the Inquisitor's combat-oriented abilities for a replica of the Summoner's Summon Monster ability. I like the idea of playing a summon-focused character who has a broad skill set and a fresh spell list.
While I doubt I'll ever play it, I can respect the thought behind the Unwavering Conduit, an archetype for Lawful summoners. In exchange for more restrictive skill point allocation rules and an alignment-bound Summon Monster ability, it boosts the Eidolon's saves, which I understand to be one of the Eidolon's major weaknesses.
I also like the Herald Caller archetype for providing four skill points a level.
The book also offers support for counterspelling in the form of two feats that boost dispel checks.
If you're curious what the book contains, consider looking at the Monster Summoner's Handbook section at Archives of Nethys.
Morphic Savant is my favorite thing to come out of the book. Besides offering new ways to make Proteans more palatable in the early levels, it allows you to make sure you have the best eidolon for your group's needs on any given day. This is especially useful in PFS where you never know what your tables are going to have.
Most of the archtypes add an awesome summoning spin to old classes. Sadly, the Ancestral Harbinger has poor bonus spells/spell-likes and the Unwavering Conduit feels like a straight downgrade on all fronts.
Like the extra flavor for Planar Binding/Ally. Helps make it more of an event when you cast it.
I flipped through a copy at the store, but really didn't see anything too useful for my conjuror wizard. Did I miss something?
Augment Summons, Superior Summons, and a means to get summon monster as a standard action is all you need to really excel as a monster summoner. A0 lot of the book is for flavor, archetypes to let less SMX friendly classes hang with the big boys, and a few interesting anti-summon tactics/options.
I'm currently running a Herald Caller with Augment Calling in an Rise of the Runelords and having tons of fun!
You do have to ensure that you are not stealing the show with your powerful outsiders though! But it can be very versatile and when another player have died they have temporarily taken control of the toon I was bringing.
So lots of RP moments and a very powerful and versatile ability. Oh and the extra skill points means you can do more stuff early on as you lack the spell slots to deal with all the things.
I can highly recommend that archetype!