The Power of SHAZAM! had several major WTF moments for me, not just in characterization, but some of the plot devices used in that series. Here's a list:

The "four year gap" between the GN and the series.

Shazam, rape victim? (remember, Shazam's supposed to be the father Superman's foes Blaze and Satannus)

The "Billy Batson - SuperTeen" (thanks, Marvelozzo) Adult-hero-kid's-brain version of Captain Marvel

Mary Batson spending half her time acting like a spoiled little rich-b!tch with a massive case of reverse PMS and the other half as a wimpy whiner. (In fact, the whole series had a lot of whiny characters, especially Billy and Freddy. Yeesh)

Freddy Freeman... cocky jock

Cap, Mary and Junior sharing the powers of Solomon, Hercules, Atlas, Zeus, Achilles and Mercury.

Adult "Lady" Cap instead of young Mary Marvel, which switched the "family" dynamic from big brother - little "brother" - little sister to Father - Mother - Son. This was caused by an implied "mystical incest" between Cap and Mary that "give birth" to a Junior that flailed and squirmed like a newborn when the lightning first struck him.

Dudley the drunk traitor (he "unintentionally" offered up Mary to be killed by a minor demon)

Tawky Tawny, Pooka. (according to Irish myth, Pookas are the most dangerous critters in the Faerie realm. I don't care how many times someone says "Pookas are playful and mischievious like Harvey", the fact remains that they ain't)

CM3 (the less said about this bit of "modernization", the better)

"CM3" punching Mary in the face... twice.

The Invasion of the New Gods (Cap and Mary using Mother Boxes to summon the magic lightning when, a few issues previous, Shazam told Cap that he didn't have to be at the Rock of Eternity for the World's "Mightiest" Mortal to change back into Billy)

The Starman and GirlFrenzy crossovers: "But - but I'm a hero!" (Cap) "Don - don't kill him!" (Mary)

Mary's "little girl" costume on a buxom, grown-up body that somehow turns from Marvel red to Vestal virgin white (flegh)

Billy, Mary, Freddy and the Bromfields all moving into Ebenezer Batson's house.