As explained in Roy Thomas' Introduction to this Marvel Masterworks volume, Marvel's Captain Marvel was expressly created so that Marvel Comics could trademark the name "Captain Marvel." The initial origin story was written by Stan Lee. The four subsequent stories were written by Thomas. All five of the initial stories were illustrated by Gene Colan.
These stories do an adequate job of introducing the character. They establish a basic set-up--he's literally Captain Mar-Vell, a Kree warrior given the task of studying Earth. Mar-Vell loves Medic Una, and is hated by his commanding officer, Yon-Rogg, who covets Una. It's a bit of a Snidely Whiplash set-up. If Yon-Rogg had a mustache, he would surely twirl it every time he secretly plots to kill Mar-Vell. On Earth, Mar-Vell adopts the identity of a scientist, Dr. Walter Lawson, who has conveniently died in a plane crash on the the way to a missile base in Florida, where the Kree Sentry (recently defeated by the Fantastic Four) is being kept. There he meets Security Officer Carol Danvers, soon to become his human love interest.
It's all pretty perfunctory, relying on absurd coincidences. And you can almost hear Stan telling Roy, "Let's set up a love triangle quick, so we can give the hero a hang-up." It doesn't help that Mar-Vell (dubbed "Captain Marvel" by the Earthers) is a pretty generic superhero. He has super strength (aided by Earth's lighter gravity and his Kree battle-suit), can fly (when he wears his Kree jet belt) and has a wrist-lens uni-beam that blasts stuff. None of this is terribly exciting, by superhero standards.
Still, Roy Thomas and Gene Colan managed to make Captain Marvel interesting in the few stories that they worked on. If they'd stayed on the book it might have developed into something more than its rather generic debut. But then the Captain Marvel comic book was handed over to a new creative team, Arnold Drake (scripter) and Don Heck (illustrator). When they took over the book, it felt like it regressed 10 years.
Heck's artistic style, while it may have been fine for romance comics from the '50s, was never quite right for superhero comics. It was certainly not right for a space-faring superhero like Captain Marvel. He just couldn't do those outer-space vistas they way a Gene Colan or a Jack Kirby could. He's not much better with human figures, either. His male characters look like boxes with limbs. He also has a tendency to put large, black splotches on the faces of his male characters. In one case (Issue # 6, p. 17) he depicts an Air Force general with black splotches up and down both sides of his face and on his forehead. I guess that they're supposed to be shadows, but they look like someone went crazy on his face with a mascara brush that morning.
On top of the black splotches, he gives Captain Marvel a jutting chin. In some panels Mar-Vell's chin juts out so much it lines up with his nose. In others, it seems to jut out even further than the nose. It's only something you notice when he draws Mar-Vell/Lawson in profile--but once you notice it, it's hard to unsee it.
Arnold Drake's stories make you realize just how good of a comic book writer Roy Thomas was. Drake's favorite plot is having Mar-Vell battle a giant. Mar-Vell fights three giant monsters (although one is only a hologram) and one giant robot in five stories. It gets tiresome after a while.
If Drake needs something to advance his plot, it just appears. If he needs a hospital X-ray machine that somehow fires X-ray blasts, so be it. If an entire amusement park (with no paying guests, apparently) populated by automatons comes in handy, there one is. My favorite plot development is discovering that the late Dr. Lawson had built the aforementioned giant robot and, to test the killer robot out, "Lawson instructed it to hunt down and kill--HIMSELF!" Smart move, Mr. Brilliant Scientist.
The cringiest part of these stories is the sexism, exhibited not just by Mar-Vell but other charcters as well. Perhaps the most telling line in this collection is when Yon-Rogg, accusing Mar-Vell of cowardice before a mission, sneers, "Perhaps you would PREFER to stay behind to protect the WOMEN and provisions!" Or maybe the most telling line is when Mar-Vell, as Dr. Lawson, tells Security Officer Danvers, "Naturally psychological conflicts must arise when a beautiful young woman is asked to play at POLICEMAN!"
Fortunately better things were to come for Captain Marvel. He'd get a better haircut. He'd ditch his Kree Captain's uniform and get a snazzy new costume. After Jim Starlin took over the strip he'd become Cosmically Aware and battle Thanos.
And, best of all, that woman he accused of playing at policeman would become Captain Marvel herself and get her own movie!