Yes, he has fantastic ideas and his attention to technical detail is striking, but his writing is really simplistic, and his characterizations are little more than outlines.
Of course, he's part of the old s/f "plot-must-be-foremost" school of thinking, so one can hardly condemn him for being a product of his environment. For that matter, much of his writing from a few decades ago likewise clings to the "women are girls who stand by" s/f meme, too. His later stuff improves upon this, though it's hard not to notice it while reading from the perspective of today.
But I've read
Rendezvous with Rama,
2001: A Space Odyssey,
3001: The Final Odyssey, and most of his collected short stories, and the plot-is-primary pattern holds true across all of them.
Even more jarring, I notice that he falls into conspicuous (and ultimately unhelpful) repetition of words and phrases.
Rama is peppered with a serious overuse of "quite," along the lines of
Norton was quite sure that he'd exhausted every possibility. It would be quite a while before he could get back to the ship. Meanwhile, his crew couldn't quite figure out what had gone wrong.
(That's not a real quote, but you get the idea). Other examples abound; I don't have the texts with me at the moment.
Fans might defend this habit of repetition as deliberate, perhaps intended to evoke a certain thematic flavor, but in practice the effect is somewhat clanging. IMO Clarke should have picked up on this himself, but at the very least his editor should have stepped up and addressed it.
He's rather good at futurist writing, in which he posits what technology or discovery will have been achieved by the time his story takes place. Of course, the HAL 9000 didn't go online in 1997, but in other ways Clarke creates a future (now our past) that seems to hold up pretty nicely against the way things really unfolded, tech-wise. Bravo to him also for rejecting the notion that a human body would explode in a vacuum; he correctly describes the boiling-away of the body's fluids, even when the myth of explosion persists in some circles to this day!
Clarke's strict adherence to the known limits of physics is admirable, and he goes to some length to establish why such-and-such a law prevents such-and-such an action in the real world. For my money, his greatest technique as a writer is then to diverge from that established reality, because it's all the more world-shattering (e.g., the Star Gate in
2001, or the reactionless drive in
Rama) when the "impossible" phenomenon finally takes place.
Overall, though, I'd hoped for something more sophisticated than a tech manual with a pair of cardboard astronauts pasted to the page.
Oh, and Clarke has famously backed those cold fusion guys from several years back, so he loses a few points of credibility for that reason!