I know a lot of people hate this game, but bah, it's good. It looks even better when you consider that this is a launch title for the PC Engine that released in 1987. For '87 it's a pretty good looking game, visually! The graphics are a lot better than, say, the other Hudson sidescroller on the system that year, Bikkuriman World. Really, my only "complaint" about the graphics is that Hudson didn't improve their TG16 platformer graphics all that much over the remainder of the generation... ah well. But that's not an issue with JJ & Jeff, certainly.
Otherwise, my main complaint would be that the game is a bit too hard; it really should have had saving, or at minimum infinite continues without needing to use a somewhat tricky continue code that you can mess up. And if you mess it up, it's back to the beginning of the game with you! Backwards warps are also a bit overly cruel, and of course those stupid hidden keys you must have in order to finish the game are awful. I haven't gotten near the end of the game yet, even though I do like it...
Gameplay-wise, it's like Adventure Island, but with, on the bad side, backward warp and those stupid hidden keys, and on the good side, an actual lifebar and more graphcial and music variety. Yeah, I know that a few things don't kill you instantly in Adventure Island and only drain your food bar, but most kill you in one hit. This time your life bare is an actual lifebar, and it's a big improvement. The vastly improved graphical and music variety over WB/AI is great too -- the extreme repetition is one of the issues I have with that game. It's tough for me to compare this game to that one, though; Wonder Boy is a classic that I've never liked very much (the Monster World and Monster Lair games are fantastic, but not the first game.), while JJ & Jeff is a mostly disliked game that I find average, but fun. Which is the better game? I'm not sure.
(Oh, and I don't care for the potty humor, that's never really been something I like. But it's a decent platformer even so.)
