The Kickstarter for the ACKSPC released what is basically a final draft of the text pre-formatting and artwork today. Some of the new spells are pretty neat; Burning Hands is a reasonably competitive 1st-level offering for elementalist mages, there's a nice 4th-level multi-target healing-over-time spell for the priestess class, and bladedancers got Swift Sword (two attacks per round for a short duration, which is really really nice), but the summoning spells take the cake. The standouts here are Summon Berserkers (calls four berserkers from the afterlife to fight and die for you), Summon Fantastical Creature (summons any one of a wide variety of wyverns, gryphons, unicorns, and so forth), and Summon Hero (which summons a 4nd-level fighter with good stats for a short duration).
I think what I like about these is that, in addition to seeming 'powerful but reasonable', they're very Magic the Gathering-esque. You're summoning things you might plausibly meet in the game world, rather than celestial dire badgers or other extraplanar weirdness. Technically, the things these spells summon are extraplanar in origin as well, but... they're normal. Which implies that other planes are reasonably normal (beyond the usual hell and heaven-type planes). This is a refreshing break from the hidebound, alignment-enforced planar weirdness that 3.x inherited from Planescape. It encourages GMs to create their own cosmologies, and also to cross-pollinate between settings; if I want to steal Tim's chromata, for example, the excuse of 'they fell into this world from another in ancient days' is very, very compatible with this cosmology (not so much with the Great Wheel). Finally, it helps explain why the endgame in ACKS is setting yourself up as a world emperor rather than extraplanar adventuring; if other planes are pretty similar to this one, then (in general), why bother going there? This is not to say that other planes shouldn't be exotic, but setting up a power base on one's home plane rather than gallivanting through the multiverse is much more reasonable if there are high level foes locally and not a whole lot to gain 'out there'.
One final touch that pleases me is their use of the term 'spheres' instead of planes. I might have to steal that, for a little distance and breathing room from Planescape's cosmology and concepts.