Interesting, but can you make a Warlock that has more engaging things to do during combat than repeatedly Eldritch Blast?
Minor illusion at 1st level and silent image at will at 2nd level allows for decent illusion spamming when eldritch blast is still doing little more than a crossbow bolt. Illusions can be engaging in combat outside of damage spam. Spamming cantrips at low levels isn't exactly atypical of spellcasters though. Cantrips are also very easy to obtain on a warlock.
For example, a human tomelock with the guide background can go WIS based who swaps the skilled feat for a second magic initiate feat and at 2nd level take misty visions and lessons of the first ones (for the 3rd magic initiate feat. Skipping agonizing blast isn't a huge loss at that level and the book of shadows will pick up the bonus damage later anyway.
So at second level the tomelock can looks something like this:
CANTRIPS
Warlock -- eldritch blast, minor illusion, prestidigitation
Book of Shadows -- light, message
Magic Initiate (primal) -- druidcraft, resistance
Magic Initiate (divine) -- thaumaturgy, guidance
Magic Initiate (arcane) -- mage hand, friends
SPELLS
Warlock -- hex, shield, sleep, detect magic
Book of Shadows -- alarm, unseen servant
Magic Initiate (primal) -- faerie fire
Magic Initiate (divine) -- bane
Magic Initiate (arcane) -- thunderwave
SLA's -- silent image
Adding options like that isn't hard and we don't need to be that excessive. The only significant drawback to the UA warlock is access to higher level spells is only available through mystic arcanum so a player is forced to cycle through mystic arcanum for that access.
EB spam isn't something that somehow becomes more prevalent than before. The number of spell slots from the UA is favorable over pact magic short rests unless 3+ short rests were consistently available (other than low levels but other cantrips and sla's cover that) and the UA warlock has more spells known. That creates more competition for choices within the action economy.
What I'm going to play with next is a melee build and see how that plays.
Looking at what
Ashrym just posted before your post...how do you conclude that's not a whole ton of cool stuff to do during combat that isn't Eldritch Blast?
TBF, the rate of access to higher level spells does have a negative impact. It's kind of noticeable when all your spells slots can go to 3-5th level spells under pact magic and only go up to 2-3rd level spells in the same level range. Trading off higher level spells for a more lower options is a loss of options at those levels.
It's one of the reasons I requested more invocations in my feedback to cover it a bit better.
If we couldn't cycle through mystic arcanum for some of that access the newer model would be a hard pass instead of workable with some growing pains. I suspect trying an EB/hex spammer build and a melee build is going to be a different story without the invocations going towards higher level spell access at first. We'll have to see.
Should've stuck with a short-rest recharge and just given them more spell slots.
...
Book: HECK YES. Great design choice to allow the Warlock to swap out two cantrips and two first level spells with an hour's preparation. Adding Int or Wis to all cantrips is also pretty crazy good... especially since you can also get agonizing blast and do 1d10+Int+Int. Gift of the Protectors is kind of... Death Note Inverse which feels less "Warlock" to me but... uh... whatever?
There are spells that would need to be adjusted on the arcane spell list to accommodate the short rest recharge mechanic. Animate dead during downtime or wilderness travel for example. Shared spell lists creates issues over individual spell lists because of mechanics like short rest recovery when the spells were designed with long rests in mind.
The book of shadows allowing for changing cantrips and rituals via short rest is something I do like better than hunting down rituals. I can basically do any 1st level ritual spell for 2hrs instead of 1hr as the worst case practical effect. Agonizing blast and the book of shadows bonus doens't stack for damage though.
When you reach 5th level as a Warlock, this spell also enhances other cantrips while the book is on your person; you can add your Warlock spellcasting ability modifier to the damage rolls of any cantrip you cast that doesn’t already have that modifier added to its damage roll.
Agonizing blast already adds that modifier so having agonizing blast becomes pointless with book of shadows.