It doesn't happen too often that a second season (second installment, sequel or anything of that kind) ends up being just as good, if not honestly even better, than the first one. As a matter of fact, a lot more frequently it's just the other way around and the quality declines (more or less drastically, depending on the case) with time.
Luckily, though, there *are* exceptions, and this is exactly one of those, since "Yappari Oshii Keiji" was, imvho, even better than the original "Oshii Keiji".
Having twice the number of episodes as the original series might have had something to do with that feeling, since the tremendously good writer, Uda Manabu, had more room to have fun with continuity, inside jokes etc. etc....whatever the reason, it was a true viewing pleasure from the first to the last minute.
A great script with nicely intricate mystery plots and lots of seriously hilarious comedy, a very convincing performance by the whole cast (with particular praises for the brilliant Kazama Shunsuke, for the lovely Shiraishi Sei and - although she guest-starred only in one episode - for the simply wonderful Kurosaki Reina ^___-), a nice and catchy score, good direction and photography...well, what's not to like?
Perfect 10! ^___-