Our Venerable Lord Kroak has dropped in power dramatically. Last edition he was 1225 pts and now he is 600 pts. And not worth those points unless you are playing a very high point game.
He no longer can cast anything but Deliverance of Itza, making him at best an extremely expensive bomber, since the spell is cast in a radius centered on Kroak. He is more survivable than a normal Slann, but you lose the benefit of.. oh I dont know... actually being able to cast more than 1 spell. He no longer can possess other magic users either, again limiting his effectiveness. Basically, instead of having a Slann with extra powers, you instead have a 1 trick pony and you're still going to need a Slann.
Overall a net win for points (you should be able to squeeze in a fully decked out Slann Mage-Priest within the 625 pts you are saving from last version), but ultimately a waste of points for most all purposes.
Now, if you have points to toss around all willy nilly, you can take advantage of the two footnotes that are special to Kroak. 1 - You can add his 4 Power Dice to the army's general power pool. This could be a great boon for your *actual* spellcaster to fire off some serious magic (oh how mighty Kroak, the best magic user of all time, has fallen when he is just a power dice battery). 2 - You can make Kroak's unit of Temple Guard Unbreakable. Which is handy if you intend to actually use his 1 spell, since you need to be in the middle of the battle to do any good with it.
In my opinion, our mighty Kroak has fallen pretty low. He's essentially a power dice battery for an actually useful Slann. He's too many points and too limited in scope to perform in a normal game (2000 or 2250 points), but you might toss him into a higher point game if you are going full on magic mayhem.