Okay, at best. In the classic X crossed with Y, it's virtually a mashup of Chobits and To Love Ru, but not as good as either. I got the distinct impression that the writer had those specific works in mind and was trying to split the difference. At least our protagonist, Takeya, is more likable than Hideki of Chobits, but that's damning with faint praise.
For those unfamiliar with DearS, it takes place a year after an alien spaceship crashes in Tokyo Bay, disgorging leigons (or at least 150 or so) of very friendly,
extremely attractive humanoids. Mostly female, apparently. Takeya, who is apparently the only person on earth who's suspicious of them, ends up rescuing one of the DearS whom he finds starving on the street. She pretty much promptly starts calling him Master, and declaring that she's his Slave, a situation he doesn't like one bit.
Reportedly, this anime shed most of the sci-fi elements that were in the manga, but as I have yet to read that version, I couldn't tell you how it changed the story. I strongly suspect that there was significantly more background to the culture of slavery than was revealed. Too many unexplained references to their culture were left dangling. The roles of Barkers/Biters, for example. Possibly Diplomats/Warriors, but who knows? Not me.
I found the whole experience rather uneven. There were a number of parts that were well done, even charming. And then... oh, but then... Significant parts were obnoxious as hell, the worst offender being the entire character of Mitsuka-sensei, and everything having to do with her. I don't even want to get into it, except to say that at least once, in a blatant attempt at lampshade hanging, her students wondered how such a wholly inappropriate and absurd person is allowed to be a teacher.
On the flip side of that coin, the audience is often given enough credit that they can read between the lines, and infer things that are going on without having to have it spelled out. I feel that the best example of that is a whole subplot where
Spoiler
Miu's host family won't allow her to lift a finger to help out around the house. Being (secretly) a willing slave with a compulsion to serve, this leads to a growing sense of frustration, which is never discussed, but is entirely shown by how it colors her behavior. The plot is resolved with a friendly chat where her host explains that she and her husband were never able to have children, which is one of the motivations for taking in a DearS. It is left to the viewer to figure out that Miu's later sense of relief comes from her realization that by letting them dote on her, she's fulfilling a much deeper need than mere housework.
It's pretty heartwarming.
My biggest complaint, (eh, second biggest, after Mitsuka-sensei) is the reveal at the end, where Miu flat out explains to Takeya that
Spoiler
the DearS are a slave race completely incapable of independence or even basic decision making
which runs counter to all the wants and preferences we've seen multiple characters express throughout the series.
In short, if like magical girlfriend plots with a hefty dose of eichi, you may like this. But if you haven't seen To Love Ru yet, go watch that instead.