Well, our core units are expensive, but so far I had a blast building lists and trying out Ravagers and Cabalists (looking forward to trying Despoilers as well). There are just so many different things to try out, with relatively similar models used, it's insane.
And I got to say, my lists have been doing pretty well (though I only played friendly matches at home, so far and we all just started AoS in May).
The Ravagers are awesome because the mere possibility of spawning marauders in the backline, keeps the opponent on edge (literally!) and the Cabalists (tried them out with that old Bloodthirster as Be'Lakor before I bought him) were really good at casting all those juicy spells.
Also, some of our synergy/MvP models are really cheap for what they bring to the table. Sorcerers on foot, awesome ability + awesome built in spell + mark bubble for 110 points is a steal.
The command ability of the Chaos Lord on foot (target unit fights in hero phase) is just beastly if used on the correct target (like 40 marauders or... Archaon!), and he is also only 110 points (iirc).