This isn't a "good" RPG by any stretch of the imagination, but I have to give the original designers credit for actually trying to make a real game out of it. Though the gameplay could use some work, the design philosophy does legitimately seem to be "cohesive game first" with the hentai bits added in around it. And speaking of the hentai, they even got ambitious with a form of interactive sex scenes that it's possible to mung up if you mongle around too much. Again, nothing amazing here but at least a somewhat higher standard than most formulaic hentai "visual novels" were aiming for at the time.
The story can't be said to be one of the strengths, however, that's just silly nonsense from beginning to end. The setup is that you're J.R. Hardtop, Florida's best private dick, and you head out to the fictional Cobra Island at the request of your old friend Faythe when a scientist friend of hers goes missing. You're not long on the island before a gang of goons tries to extort you (by way of a telescope overlooking a nude beach) and you have to shoot 'em all up. Making your way to Faythe's house, you learn the gang is part of this weird para-military organization called Cobra that has co-opted the police department and taken over the island. For whatever contrived reason, the Feds can't come out and deal with one of their territories being overrun by a hostile force, so instead J.R. and Faythe will gradually overthrow Cobra while also searching for the missing Donna.
(As to who the girl is shooting up your screen in the introduction, I still don't know. The secretary from the construction company maybe?)
This actually first came out on the PC-98 in Japan; that version had a standard menu-based RPG battle system, but when Megatech ported it they revamped it so that it has a quasi Active Time type system and you also have to find exposed enemy weak points to do better damage. Outside of a couple of bosses, the enemies are consistently a joke, so this isn't a big deal. But it's at least a new and ambitious idea, and the battle graphics are at least nicely drawn to boot (looking markedly better than the low-animation sprites and low-res backdrops of the world map).
For the most part, the quest progression actually makes sense and follows logical threads. Once in a while the old visual novel "click on everything available" canard pops up but I was surprised to find the overall layout of the game was actually fairly well thought out and didn't require arbitrary solutions or re-visiting an old area for no discernible reason. The only major gameplay issue is that there's virtually no challenge until the back half of the game; two particular bosses actually manage to put up a stiff fight and might overwhelm you if you come in without an appropriate inventory or underleveled, and there's a few dungeons toward the end that are mazelike and at least test your memory (or willingness to draw a map).
Even though the plot is stupid and makes no sense, it still comes off decently as the game has a comedic tone, similar to Knights of Xentar or the Rance games (minus the habitual sexual assaults of the latter). The non-serious atmosphere also helps it get away with an Engrishy translation that is really pretty bad.
Finally, let's talk about the porny content, since that's likely what you're here for. Cobra Island is divided into four segments, each of which has a series of plot elements to work through leading up to a boss battle. After the boss battle, you get a phone number of a girl you just rescued ... call it and you meet her for the interactive sexing. You proceed through a series of two or three scenes with each girl; in each you have to choose hands, lips or toys from a menu and click them on appropriate erogenous zones to work the girl into enough of a frenzy to move on to the next scene. The catch here is that there's a "life bar" that will decrease with errant clicks, and some girls don't care for getting too kinky and will end the encounter immediately if you come at them with the hot wax or try to stuff the vibrator in their mouth. Too beta to bring the early '90s anime girls to a moaning climax? No worries, you get unlimited attempts with no penalty ... just call 'em again from JR's home office.
Aside from the four interactive scenes that gradually unlock, the other perv content here consists of two automated scenes you get by paying hookers while your assistant is off doing something else at certain points in the plot, and the more typical static hentai pics which you can collect by stealing panties from random people's houses and trading them to an otaku perv who conveniently lives right down the street from your office.
I don't have any problem with hentai games, obviously, but for those who do this one leaves you unusually little moral basis to complain. All the hero's diddlings are consensual, with the bad guys the only ones doing any unsolicited cuddling (and even then it's kept off-screen). No lolicon, in fact whoever drew this one really seemed to have a penchant for full breasts. No blood, no monsters, no scatological stuff, no animals. Interestingly, almost all of the sexual content here is actually optional. You don't have to ever call any rescued girls, you don't have to collect the perv pictures, even with the nude beach telescope at the beginning you could theoretically exit out of it without looking around. There's only a small handful of story-based titty shots forced upon you that I can think of, the most explicit of which is a masochistic mini-boss who ties herself up so you can beat on her.
I know this is a case of the bar being really low, but Cobra Mission looks downright inventive and polished compared to other hentai stuff of the period. It's still not consistently enjoyable due to the total lack of challenge combined with a lot of pointless-feeling ambling around, but at least it's capable of being amusing at times and looks like some effort was put into it.