That was a fun book. And because it was a fun book, I am going to try my hardest not to critique it as if it were something it's not. It's really just a grab bag of ideas for additional D&D magic. It has a niche and it fills it effectively.
The only ambivalence I feel is my growing realization that the last thing AD&D needed at this point was more material for wizards and priests. They already got half the Player's Handbook, they really didn't need one of the line's first and most prominent supplements.
But that sort of thinking would lead me down the long and meandering path of questioning AD&D's overall editorial strategy, and that's something that is better suited to a post near the end of the line. Instead, let's just take it as given that more stuff for wizards and priests is a good thing.
Even so, the Tome of Magic is not entirely unproblematic. It introduced Wild Mages, which, you know, are a thing you're either on board with or you're not. You cast spells! But every time you do there's a 1 in 20 chance that something really wacky happens instead! It's only a matter of time before you're killed by your own folly!
I don't count Wild Mages as a flaw, though. They have an audience, and that's who they're here for. The book's flaws are more subtle than that. There's a spell. It's called "Know Time." You cast it and you know the time, rounded to the nearest minute. As magical powers go, it's unimpressive, but it has its uses. There are situations in which it might be handy to magically know the time. But then you take AD&D's magic system into account and there are no circumstances under which you would ever conceivably use this material.
At the start of the day, pray for 10 minutes to the God of Time. In exchange, once, at some point in the future, you'll know the correct time. And that's one of, at most, five spell slots that you have to give up to do it. An interesting and flavorful ability is doomed to be wasted word count because the realities of the game make it unworkable.
The other subtle flaw with this book is the way that its new spells seem to muddle the already nebulous line between "wizard" and "priest." And perhaps this is as it should be. Historically, most "magical" traditions have also been "religious" traditions and even today its difficult to engage the mystical without also exploring the spiritual. But D&D has always drawn an arbitrary line between the two, and now, with new Priest spheres like "Time," "Thought," and "Numbers" you can easily build a Priest that is straight out a historical Hermetic practitioner.
It's subtle, because that isn't even really a flaw, per se. It's just that once you start down that road, you've got to put a lot of effort into warding off the crushing existential realization that D&D's classes don't make a lot of sense. And having a few dozen extra spells is barely worth it.
The Tome of Magic also includes a bunch of new magical items. Some of them, like the amulets that replicate metamagic spells, are fairly bland, but most are pretty good and there are a few genuine gems (like the Mist Tent - it's a cloud you keep in a bottle and when you let it out, you can sleep in it like a tent). It was a little awkward when some of them turned out to be better Artifacts than the Artifacts in the Book of Artifacts (Like the Quill of Law, which makes any legislation written with it and passed through official channels magically unbreakable), but that just plays into my intuition that "Artifacts" are really just magic items with a PR department.
Overall, Tome of Magic is a good addition to an AD&D game, if you can handle the damage it does to the AD&D rules. It was one of (if not the very first) rpg supplements I came to own, and so I'll always have a soft spot in my heart for it, but I'm not actually sure the tradeoff is worth it.
UKSS Contribution: There are a couple of . . . unique spells in this book. They're sort of like . . . anti-illusions? Nega-illusions? Inverted illusions?
Whatever you want to call them, they pose serious ontological questions the book isn't prepared to answer. One is called "Solipsism." How it works is that you wish something into existence, but it isn't "real." Most people can't even see it. But if you put in the effort, you can force yourself to believe. This works just like a savings throw vs an illusion, but if you succeed, you believe in the spell and can interact with the created object just like an ordinary thing.
The other, similar spell is called "Disbelief." It allows you to take a real object and disbelieve it, just like an illusion. If you do, it disappears from your reality. You cannot interact with it in any way, nor it you. You could walk right through it, if you wanted to.
I feel like those spells are on to something. Some odd and unnerving school of magic that involves creating your own elaborate fantasy world and then making it overlap with the real one. There's potential there, at least, for a take on magic that is rooted in a very different worldview than D&D wizardry.