Let's be clear. Bokusatsu Tenshi Dokuro-chan is NOT a plot-driven anime..it quickly introduces the reason for Dokuro-chan's existence in our world and the rest of the series is essentially Dokuro-chan ruining Sakura's life as he tries to get by in middle school.
In terms of what is actually good about the show, I'd say it's the comedy that really shines. Sakura's body has no limit to the amount of torture it can take, whether it be getting his eyes squeezed, the top half of his head cleaved off, or his "vital regions" getting violated by a switch-activated mass of tentacles. One can only imagine how this kid reacted when he was first killed..
The show itself also gets its humor from the occasional ecchi scenes that escualte with no warning whatsoever. One minute Sakura finds Dokuro-chan trying to keep him warm, like any typical foreign anime babe, and the next she's in all these suggestive poses listing the ingredients she used in Sakura's Valentine's Day chocolate. The scenes can sometimes be downright uncomfortable and horribly timed, case in point Dokuro-chan grinding on Sakura's nude frontside while the two just happen to be dangling over a freakin abyss.
The episodes themselves are relatively inconsistent with one another, broken into 13-minute mini episodes. This obvioulsiy can make it a pain to find them online, with episode 3 either meaning 13-minute episode 3 or 26-minute bundle episode 3. They usually deal with plots commonly found in slice-of-life romances, like Valentine's Day, bathing suit-anything, and confessions of love, but with Dokuro-chan risking to ruin everything with her innocent mannerisms.
The characters are subject to breaking out of character, and it's often difficult to tell just what their "regular" personality is. Dokuro-chan can go from the naive moe chick from another planet to overprotective and sadistic in a matter of seconds. Sabato-chan is introduced as Dokuro's rival and an violent, dedicated angel but often, especially at the end of multiple episodes, she's seen as a impoverished and pitiful soul that you just want to hug and offer a warm meal. If anything, the only character who actually STAYS in character is Sakura's crush Shizuki-chan, who also just so happens to be the biggest deadpan of the series.
All in all, Bokusatsu Tenshi Dokuro-chan is a hilarious but extremely unpredictable show. It takes a spin on school life anime with over the top violence, fanservice and the occasional fantasy element. If you can dismiss the lack of a recurring plot, I'd say it's a good choice if you're looking for an anime to get a good laugh because this one puts the "slap" in slapstick. Pipiru PiruPiru Pipiru Pi!