Didn't Castlevania nes had awkward game play, that it got improve only on Castlevania 3 and to get perfect later on Super Castlevania?
There's nothing awkward about the original Castlevania. It's a calculated experience from beginning to end, meant to be conquered with precise positioning and calm, collected play. The sub-weapons accommodate the bits that feel insurmountable, not that anything actually is. It's a very methodical game, and painstakingly clever in design.
The Adventure has real, substantial problems like input lag and pixel-perfect platforming, but I'm quite fond of it in spite of the potential flaws. You can still learn it, and it's brimming with personality. There are really novel concepts in the level design, like the entirety of stage 3, that have not really been revisited anywhere else in the series.
Belmont's Revenge is of course the realization of the promises made in The Adventure; it truly stands among the series' best, without sacrificing the unique flavour established in its forebearer. I'm really hard-pressed to think of a better Game Boy game. The music shouldn't be able to exist either, but it does, and it's supreme. It's a small miracle in all respects.