I don't know where to start with Dr. Chaos because it is such a strange game. It is an action-adventure game developed by a company called Marionette, whom as far as I can tell hasn't made any other games that people in the US have heard of. In Japan it was released on the Famicom Disk System, published by a company with one of my favorite names, Pony Canyon. Of course, in the US it was released on cartridge for the NES, so it was one of those games that you could save in the Japanese version, but had to remember passwords for the US version. One thing that was surprising to me was that the box art for the US and Japanese version were basically the same, and it pretty much depicts the stuff that is in the game, which I think is rare for a 1988 NES game.
The most striking thing you'll notice when first turning Dr. Chaos on is the really good music. It really capture the haunted house, sci-fi, horror feel they were going for. For me, there was something familiar about the melody, and I didn't figure it out for quite a while, but it sounds like the bass-line from Phantasmagoria (nevermind the stupid video footage) by 90's visual kei band Baiser. Of course, the song came out ten years later, so if there was any inspiration, and I doubt it, it was coming from Dr. Chaos. The music that plays when you're on one of the pathways to a boss is also really nice.
The best way I can think to describe Dr. Chaos is “a Castlevania game mixed with a point-and-click adventure.” You enter a spooky mansion and it is filled with doors and rats. It's a side-view and the controls are pretty solid, so you stab the rats and enter the doors. When you go in a door it goes into a point-and-click adventure setup. Here you can open doors and cupboards, pick up items, turn different directions, break holes in weak walls, and enter doors and holes. The general goal of the game is to enter all of the hidden areas that are pathways to bosses. Once you go through the platforming part and kill the boss you get a part of a final weapon that is needed to kill the final boss.
Essentially, you search all the nooks and crannies of the mansion looking for these things. Even when you don't find a pathway to a boss, you are generally rewarded for opening things with items. There is pistol ammo, machine gun ammo, grenades, and potions. The first three make killing enemies much easier than it is to do so with the knife. Obviously, potions heal you. But, not all the time are you rewarded for opening things, because sometimes monsters will jump out, which forces you out the door you came in so you can fight them. This adds a certain level of tension to the point-and-click parts that would otherwise be boring.
Playing the game again for the first time in quite a few years, I was surprised that I liked it. I remember thinking it was just a goofy game where you click randomly on walls. It must have been the weird name and general strangeness that turned me off to the game when I was younger, but playing it now I really got into it. Sure it is difficult and an oddity, but it the controls felt good and I am a big fan of exploration. Maybe I've just played so man bad NES games lately that I'm not used to playing a capable one like Dr. Chaos.