So, my first thoughts about the book are:
You will see a lot more variation in HE core lists: HE core has generally been MSUs of archers, blocks of spearmen or a mix of both. The new book has some nice unit buffs that may encourage taking larger blocks of archers (hand of glory to increase BS by D3). Monday's Bad Dice Daily even mentioned using 3x3 blocks of archers (as opposed to 5 wide) with the martial prowess rule to have a really small footprint. You will still see blocks of spearmen for steadfast, but with the decrease in points cost for Sea Guard, you will see them more often as well to benefit both from the unit buffs and the large blocks. On top of these changes, I know I expect to be fielding units of 5 Ellyrion Reavers as core. I was already fielding them as special to hunt warmachines and now, I can do it as part of my core tithe. With the addition of Reavers and Silver Helms as core, you may see entire "Swift Strike" calvary army builds as well. I could conceive of an entire army meant to pick off the opponents artillery and BS shooting and then run circles around the other elements of some armies. (wouldn't work well vs. VC or Skaven though).
The HE triad (Swordmasters, White Lions, and Phoenix Guard) only got better particularly from Martial Prowess. The SM and White Lions went DOWN in points and the Phoenix Guard were neither nerfed in any way or moved to rare. So, players who were already using them will not stop using them. Now, all HE can attack with 2 supporting ranks instead of 1. The WL and PG are often taken in blocks 5 wide and 4 or more deep, so it is a change of 10 attacks to 15 (at S6 and S4 respectively). Also, as a minor aside, you are more likely to see Shadow Warriors with their lowered costs, but their rules are still unchanged.
High Magic - Expect to see this lore. The LVL 4s could cast 4 or more spells on 2 dice a piece fairly easily (with High Magic, they have an innate value of 5 with many spells requiring a 5 to cast. They will use 2 to avoid the broken concentration and throw their last spell with 1. So even a large archer mage bunker could have a 3+ ward save. A level 2 may be used just for the Signature spells (drain magic, and the 2d6 S4 magic missile) to improve a ward save by 1 or 2 points.
Loremaster, Sea Helm, Annointed, Handmaiden, and other non-Special Character Lord and Hero options - I honestly don't know what to expect from these yet. I think the key word is "options". A lot of differently themed builds can be bullt around these options.
I mean the Loremaster alone is a Swiss army knife. Bunkered in a unit of swordmasters charging at a favorable target, shooting missiles from fire, light, metal, and death along the way, combat buffing and hexing with beasts, life, shadow and heavens.
Maidens - I would anticipate seeing these in shooting heavy builds, but not in overwhelming numbers. Although wonderful models, they are still basically higher BS archers with magic bows at +1 S.
Skycutters - The changes in core and to the chariots may lead to chariot builds or highly mobile builds. These in their different incarnations could make a significant piece of this style of army. The bolt thrower version may also make more frequent appearances as a support piece.
Phoenixes - The Flamespyre will make a great support piece especially against high model count armies (VC and skaven) but won't wreck hobbies. I like the rules for these and hobby centered players will use them for centerpieces. With better rules for dragons, I think you are more likely to see them on the table as well especially if there is more than one large target to have cannons shoot at.