I've always found both SCIV and Bloodlines to have some major faults visually. IV came out in 92, but visually to me it feels a lot closer to a very early gen 16-bit title from the late 80s. Just the way the blocky level tiles are constructed (I realize this has kinda been considered a Castlevania hallmark since the first game, but I never really found it appealing. Didn't like it in Rondo either), and the way the sprites look and animate, etc. For comparison looks closer to Revenge of Shinobi which came out in 1989 as opposed to Shinobi 3 which came out a short time later in 1993. It is more than the sum of its parts though and really digs into the classic horror inspirations more than anything that came out after it.
I think Bloodlines has sprites and animation work that looks better than IV, but the game's biggest issue is a general subpar use of colors. I get the feeling that whoever was in charge of handling the stage graphics wasn't very experienced working within the limitations of the hardware and its palette quirks. The palette looks very compartmentalized in that each element of the environments are given their own tiny pool of bespoke colors, instead of a more flexible approach of constructing 2-3 more universal sets of tones that can be shared and reappropriated for different elements, so as to give a more concise look and have overall better range of shading on things. That's generally what the best looking Genesis games do with an expert grasp of color theory.
There are some areas that flat out look NES-like with the approach they used, like the section with the pistons in the Germany stage.