Well Pulstar is not so hard but sometimes a little unfair. Anyway if got no problems playing it to the end. MS3 is very easy i come to level 5 with only one credit.
Viewpoint and Magican Lord are the hardest Games on Neo Geo. Viewpoint i got ended after 3 weeks of playing and the ending was dissapointing. Magican lord i failed the last Level, where u must play aganst all middle- and endbosses.
Pulstar is infuriating at times, but to me Magician Lord, Magical Drop III* and yes, Nam 1975 round out the top 3. Magician Lord needs no further explanation. Nam 1975 is crazy at home, but even in the arcades that final boss is still a huge pain to beat.
Magical Drop III I say because I always play only one credit, and I always get hundreds of thousands of points, meaning I have to face Black Pierrot as the 12th enemy, and at that point he is impossible. It truly belongs in the "puzzler impossible to beat in a quarter" category, along with Pop 'n Bounce.
I would agree on viewpoint being hard. but the thing with shooters I find is it is all a pattern. I guess you can say that with any neo game but the hardest games I have trouble with are the ones were the bosses are cheap or do not open themselves up easly for a pattern. the End boss in WH2 comes to mind. And believe it or not the Endboss of Galaxy Fight for me. Kabuki Klashes bosses also were a pain for me. these are the games that frustrate me, the shooters I can handle since I am always able to make some progress.
oh and on the puzzle side Magical drop III is a challange but I actually have a harder time with Money puzzle exchanger, although i have beat the end boss there.
On the whole I very much concur that Money Idol Exchanger is a more dificult game, but when one faces an opponent who's drop pattern is better than the final boss's, and whose cursor speed, as I read, is "basically teleport," one knows that the challenge shall be great. Ever since I went to the one quarter rule, I have never beaten the game.