Gokusen is in my top 10 favorite mangas of all-time. It had everything that I love: action, comedy, likable characters, and most of all, it let the story do its thing and didn't hit us over the head with romance. Since Deka Wanko is by the same mangaka, and tries to use the same formula --quirky characters + action + comedy--I thought for sure that I would love it. But I don't. No matter who authored it, Deka Wanko falls down in several respects as an entertaining manga, most notably with its characters.
Whereas Yankumi was the major selling point of Gokusen, Deka Wanko's Hanamori is easily my least favorite thing about the manga. Hanamori's schtick revolves around three things: that she is utterly, hopelessly stupid (she makes even shonen manga protagonists like Naruto look like Einstein in comparison), that she is utterly, hopelessly weak (the manga underscores this point by making her wear the frilliest clothes imaginable), and that she has the smelling abilities of a police dog. All of this was rather amusing for the first 10 chapters or so, but then it began to irritate me. There's nothing to this character other than her nose; by design she brings nothing else to the table as a main character (street smarts, fighting ability, etc.) I can't take her seriously at all, and don't enjoy the fact that none of the other characters (especially her partner) take her seriously either. Kirishima, Hanamori's partner is another disappointment in that he is charmless, bad tempered, and almost as stupid as Hanamori. But he's a good fighter and a bishonen, which means we're meant to overlook his bad personality. Unfortunately, as Hanamori's partner and the very predictable choice for romantic lead, Kirishima is an impossible character to ignore, as much as I would like to. Worst of all, there's little hope of either Hanamori or Kirishima ever becoming smarter since the mangaka has included Yanagi, a genius character who solves all the cases Hanamori & Kirishima can't. (Brawn and a sense of smell can only get you so far in police work.)
Besides Hanamori and Kirishima, the side characters are at least occasionally good for some laughs, though they're generally nothing special as characters. Mostly they seem drawn straight out of a "police drama 101" handbook--genius super detective, tough as nails squad leader, wise older cop, etc., etc.--but I wouldn't mind reading a series just about them before Hanamori ever joined the quad.
If the characters are the manga's weakness, the plot is one of its stronger points since the cases are usually somewhat interesting, and often good for a few laughs, though they tend to be solved rather quickly and easily. (But at least they don't drag on!) Deka Wanko is primarily an episodic manga with no larger, overall plot. (Which could be a good thing or a bad thing, depending on your perspective.) All in all, Deka Wanko is simply a mediocre manga: the plots and humor are all good, but the unappealing lead characters drag down the enjoyment factor considerably.