Here's a perfect example of the concepts not translating to the screen very well with STTMP. In the book, Roddenberry spent some time describing how Deltan women were overpowerlying sexual to human men. On the screen, we see a bald woman exuding no sexuality.
Persis Khambatta... exuding no sexuality??



Have you had your vision checked recently?
She states her "oath of celebacy is on record" with a bit of a thick accent that was hard to hear in the theater. It had no meaning. We see all the male crew members on the bridge snap their heads around to look at her and the we can't figure out why. If I hadn't read the book, this whole scene would have been a mystery.
The downplaying of Ilia's sexuality was not the fault of the filmmakers, but of the studio, which insisted on a G rating based on the absurd prejudice that science fiction is kid stuff. Given freer rein, it's a certainty that Roddenberry would've played up Ilia's sexuality very heavily onscreen. (The only other feature film Roddenberry produced, Roger Vadim's Pretty Maids All in a Row -- also scripted by GR -- was a dark sex comedy that was one of the first mainstream feature films to show frontal female nudity after the MPAA instituted the R rating that permitted it.)
The endless trip around the Enterprise in spacedock
Which meant a lot to many ST fans back in 1979, when they got to see the old girl on the big screen for the first time ever. It was an unapologetic fanwank, but the fans were entitled to one. It was a celebration of ST's return, of its arrival in the realm of big-screen, big-budget moviedom. After three decades of medium-budget films and TV shows, it's hard to realize what that meant for ST at the time.
The endless trip through Vejur (and some really bad special effects)
I find that maybe more inexplicable than your reaction to Ilia. The V'Ger flyover is still the most breathtaking, awe-inspiring visual-effects sequence I've seen in my entire life. It was brilliantly executed using state-of-the-art technology, and it still holds up as a work of cinematic art today.
Not to mention, in both cases, Jerry Goldsmith's magnificent musical accompaniment. I'll never understand how people can find it tedious to listen to that.
In the original cut, you could not tell what Vejur was (in the director's cut, they finally show Vejur for about 10 seconds)
The story made it entirely clear what V'Ger was. Knowing how it was shaped wasn't important.
Besides, it's unfair to criticize the original cut, because it was a cut that was never intended to go out to theaters. It was a rough cut that still needed to have finished effects added, extraneous footage trimmed, and the temp sound effects track replaced with a fuller version. Unfortunately the rigid contract with the theaters forced the filmmakers to release the film unfinished. So many of its flaws are due to circumstances beyond the filmmakers' control. Robert Wise hoped they would get to complete the final edit and replace the rough cut with a proper cut (since back then, films tended to stay in theaters for months or years rather than mere weeks like today), but they never got to. The Director's Edition from 2001 basically completes the film the way it was meant to be completed 22 years earlier.
The rumour that he ghosted the TMP novelization started because the French translation of the first edition had a typographical error on the title page, which left out a chunk of the correct screenwriters' and novelist credits.
Also no doubt it was partly due to confusion between the Star Trek and Star Wars novelizations, which came out two years apart. I figure people remembered that Foster had ghosted the Star ____ novel in the late '70s, but got confused about which one it was.