I had the Holy Light and was very excited about it. I knew most of the illustrations from the big book of alchemical art by Roob (that I bought many many years ago). The deck is very beautiful with its strong colours and crazy collages. But I COULD NOT READ WITH IT.
I said, okay, I'll wait for the book. And I waited for the book.
It took some time until the book came out and I started to read it. And I don't know what happened - the author's style grated horribly on me. She has such an apodictic style (is there such a word in English?), she is so sure that what she says is The Truth and everything else is Wrong and Faux - I couldn't bear it.
Maybe I'm simply spoilt by reading too much academic literature or books like Greer or Wen or Place or Huson... and many other authors who allow for an open minded approach. You don't have to follow them completely and blindly. They give you the facts and let you think.
I didn't like author's style of drawing conclusions, I'm sorry I don't even remember what it was about - but all of a sudden, my Holy Light mojo left without a trace.
I had the feeling that behind the whole facade of important mystical things and secrets that CPT promised to reveal, there was nothing but an interesting personal idea and an elaborate conspiracy theory. I was very willing to be convinced by her but it didn't happen. And then I had no joy any more with the deck.
Even the deck interview I did seemed to laugh about my efforts.
So I swapped it away (and I'm not one to let go of decks easily, I'm a Taurus and Dragon and sit on my hoard with bared teeth).
And I'm not sorry.
BUT the deck is a beauty, and if you're more willing to follow the author and don't jump to conclusions unfairly the way I did (and I did: I didn't even read the book any further after I was annoyed for the 3rd time) but really try to comprehend what she was trying to do, you may enjoy it very very much.
So if you want an interesting deck with some strange theories behind it, go for it.
Now the Tabula mundi - I don't have it YET (it's on its way to me), now if you ask me, that's a totally different league. First of all, it's not a collage of existing artwork taken from context and used to illustrate a theory - sorry to say it so harshly - it's a real work of art done by an artist who has climbed into the coronary veins of the Thoth, Thelema and esoteric teachings, done no damage there and come back to tell an exciting story.
I have seen the black and white version with my own eyes and was blown away (Zephyros has one - probably the only one in Israel), and when I see the work the artist is doing on each card, my heart beats faster.
There is a beauty and harmony and depth to it - just look at it and the synapses start firing, but not in bewilderment and huge effort to understand like with the HL, but in gratefulness and awe for giving us a picture book of the universe and this universe moves and lives.
No, there is no comparison. But the Holy Light digs into alchemy and the Tabula Mundi into Thoth and Thelema, so they're really different worlds. I just feel the TM digs so much deeper - which may be totally unfair.
Now if you want to dig into the alchemical aspects of the tarot, I think you should look at Robert Place's Alchemical. I have his book and it's scholarly, coherent and interesting. He relies on much of the same Renaissance and Baroque imagery collected by Roob in his book, but he doesn't make collages but takes them as inspiration for cards painted in his cool, understated, neo-Classical, precise style - which makes for much more visual unity than the HL.
I don't have the HL any more but I do have the Alchemical and I'm very happy with it although I didn't start studying it in depth yet (too many other things on my tarot table). But it's structured in a way that makes it easy to read even if you don't know the Ins and Outs of Alchemy - and the Holy Light didn't let me read it.
This is my biased, unfair and probably silly opinion
I know many people love their Holy Light and get good readings from it and even follow the author's theories without wishing to get up and say: now listen, that's not a valid conclusion...
:-D
ETA: I knew I'm an idiot, Aeric said it so much better and I didn't even mention Etteilla!