It's fascinating, partly because it's Rumiko Takahashi's first professional manga series and partly because it's so different from the Urusei Yatsura anime that started in 1981. I'll start by describing the Urusei Yatsura everyone knows.
ANIME VERSION: Ataru is the universe's biggest lech, who spends all his time chasing girls. Lum is the alien girl in a tiger-striped bikini who thinks she's his wife. Shinobu is a schoolgirl with superhuman strength, which she uses to throw desks at Ataru. (Maybe she'll become Mendou's girlfriend, but he's as appalling a person underneath as everyone else in this series. Takahashi eventually gave her Inaba.)
ORIGINAL MANGA VERSION: Ataru and Shinobu are fated to be together. (That had been Takahashi's original intention, until reader pressure made her change the series's focus to Lum.) They get on badly, due to Ataru's personality and Shinobu's tendency to overreact, but in their heads they're still connected and they'll both get angry at perceived infidelity. This manga-Ataru isn't a lecher! He's practically prudish. He's extraordinarily faithful here to Shinobu, showing no interest in Lum even when she's jumping in his bed and waving her top at him. He'll shout at her when she offers to share his bath or make babies. He's like a prototype version of himself, before his best-known personality trait had evolved and so the point of his character is just to be an immature, cockroach-like disaster magnet.
This makes these manga chapters far more enjoyable than their equivalent anime episodes, incidentally. In those, Ataru's a girl-chaser right from the beginning, making the show's first year uncomfortable.
Anime-Ataru makes his first appearance in chapter 8, when he tries to chat up Benten. Shinobu will accuse him of having a wandering eye, but here that's just an informed attribute that feels unrelated to the character in front of us. Admittedly one could also cite chapter 4 and his jokes to Sakura about removing her bra. Even there, though, he doesn't react to her boobs-in-face crash-bag introduction and instead behaves like a decent human being. One might speculate that his interest in women is abstract. He likes the idea of them. He might pursue them if they're in the distance. However his lechery seems to shut down when an actual woman starts calling his bluff.
Ironically, so far Takahashi's female characters have been far more extreme, flawed and funny in their relationships with the opposite sex. Lum knows no limits in how far she'll go in her pursuit of Ataru and incidentally spends half of chapter 1 topless. (Why doesn't she have another bikini top? Is she an exhibitionist? Admittedly Ataru also notices this oddity, but Takahashi doesn't go so far as to explain it.) Similarly Rei's appearance provokes all kinds of fevered behaviour from the female cast, from Ataru's mum (!) to Shinobu (bwahahaha) and a small platoon of people who happened to be passing. That's from chapter 7, which made me laugh aloud and is the funniest in the book.
Of the other characters...
Cherry takes a surprisingly major role. He's still a pain in the arse, both to the reader and the other characters, but he can also be funny. I liked his instant assumption that Ataru's dead as soon as anything happens.
Shinobu is bland. You can see why the readers petitioned Takahashi to sideline her. She exists to whinge at Ataru and she'll yo-yo between "affectionate girl who still likes him despite everything" and "hair-trigger emotion fountain who jumps to the worst conclusions at the drop of a hat". She hardly ever does anything. She's just a walking plot function. She's a nice girl, mind you, and I wish her all the best, but her role in these chapters is merely to react.
Lum in contrast does all kinds of wacky things for Ataru (although he wishes she wouldn't), frequently saves his neck and would turn the Earth inside-out to get him back. (I don't remember her ever literally doing that in the show, but she probably could.) She's great. She's also a near-lethal cook whose food causes unconsciousness, nausea and brainwipes. (If you're human, anyway.)
The art's very different to what I've been reading in Inuyasha recently. That's unsurprising. That's a thirty-year interval, throughout which Takahashi was writing and drawing eighteen pages a week. This early work is rougher, messier and more cluttered. It's still pretty good and at times even sexy, but it's the work of a very different artist with a much less complete command of form in space and of her own style. (Ataru's mother is often drawn more realistically than any other character, by the way. That looks a lot like direct observation from life to me.)
I enjoyed that. It's good. It made me laugh. I won't be reading the whole series any time soon, though, because it's 36 volumes of random episodic comedy and I've got lots of things with storylines in my reading queue. (I'd expect to find slow-burning character and relationship development if I read it, but no ongoing plot.) You're also out of luck if you're hoping to read it in English, since it's the only Takahashi manga series that hasn't had a full English translation. Viz Media started, then dropped it, possibly because it's riddled with untranslatable gags (both involving wordplay and culture).
That said, though, since it's so episodic, I could probably just buy random volumes. Dipping in and out should be fine. Maybe I could look for stories with my favourite characters? None of these are in this first volume, but I'd be interested in reading Takahashi's original take on Asuka Mizunokoji, Ryuunosuke Fujinami and maybe Ran the psycho burikko...