It seems nobody mentioned anything about wether they enjoy a versions certain particular gameplay and balance changes over the other version yet? Here's an example for the Ghost Ship level;
- as the whip guy (Trevor); in the US version at the start of the level the first sub-weapon you get is an Axe in comparison to the Japanese version a Knife. The second weapon you can get is a Knife (I think?) instead of a Cross as in the Japanese version. These changes, providing you die and don't or aren't equipped with what you already want for this level, I find really helps change things around as to how you tackle the level. I find the US version balanced things a bit better with this choice (except now you don't need Grant to access the large heart before you make it through the first checkpoint door. This this kinda screws things up). The Axe makes things much easier at the start by not have to time them stabbing skeletons at the start as your coming down to their ground level from above. While by not giving you the Cross, Medusa and the final bosses aren't as easy... Both the Cross and Axe come in pretty handy for them crows near the end if held on to that point... maybe the Axe more helpful/easier to time? So you see how by just messing around with the sub weapon placement changed things considerably tactics wise for Trevor? (Well, if your pretty reliant on sub-weapons like I am)
- for the Magician (Sypha); her first sub-weapon for both versions are the Fire Spell. I forget the rest more clearly as I've only been playing as the whipping Belmont Hero these days. But from what I recall in the US version, unlike the Japanese version, you don't get that very usefull (too usefull) homing spell for the entire level that made me rely on it to beat this stage and bosses much more easily. Combine with the bosses being more aggressive/harder in the US version (I'm thinking for the last two at the end), and I was forced to kick Sypha out and let the real Hero of this game step in and take care of business... plus figure out how to really beat the last repeat boss instead of relying of the first encounters safe spot or Sypha homing shots from a safe distance to make quick work of him in no time.

So again, playing another version of this game really made me change my tactics around quite a bit.
So yeah, this is the main reason I brought this up to encourage others to forget about what music or graphics they prefer for a sec and just play around with both versions for a new spin on things from a gameplay and game balance perspective... But talking about game graphics and sound it alright too, as I do enjoy reading what other have to say about this too. Here's what I have to say about it;
- haven't noticed anything major in the graphics department yet, besides them trying to fix the appearance of Frankenstein more in Sypha's route more by removing a layer of blocks so it don't look so much as he's coming through the walls. But instead coming along side the stairway is the illusion it gives of more, I find... still looking for something more major like what the Japanese/US version of the first Contra game scope wise (or more close too. I'm hoping...).
- in regards to the music, I so far don't mind the US version, and for the most part am really enjoying having two very different takes on the same soundtrack for added variety when playing these games (I do like the US version for sounding more retro, while the Japanese for being more refined & the original take/the true versions of these songs). So yeah, I don't see this a negative at all, but a major positive (just like how we got two different games of Rondo instead of just a port, which shockingly, is what most wanted!

I've love how Konami back in the day gave us new games instead if straight ports, like NES Life Force, Contra, TMNT2 & IV, Gradius III SNES, etc, etc. ... Besides, the SNES XX vania game rocks big time.

Well, i sure love it a heck of a lot more the Super Castlevnia IV at the moment)... the only negative thing I can think about the US version of CIII's soundtrack is that sometimes during gameplay, certain sound effects remove a certain fairly vital soundtrack channel that sometimes sounds very obvious. Like it's a bug in the game, that the track skipped a beat, or something? ... Wonder if I can remove this somehow through the wonders of emulation? ...