The middle one is easily the worst in my opinion. All black outlines or coloured outlines is consistent, mixing the two just feels a bit confusing.

It's not a question of resolution, or framerate, it's a question of timing on the frames you do have. I mean, sure, you can get more subtle motion if you increase resolution or framerate, but here's a 2 minute edit I did of your animation without redrawing a single thing:

Queens Blade/Scarlet Blade is completely unaffiliated with and unrelated to the Queen's Blade series of books/anime/games.

This looks really cool! The download links for the older versions (non-dither preserving, etc) seem to be broken though, could you provide a new link to the latest version of the 4x scaler? (assuming this new one hasn't replaced it entirely)

The most prominent (and best looking) examples I can think of in modern games are Arc System Works' more recent fighting games, the BlazBlue series and Persona 4 the Ultimate. Both games use all 2D (pixel) art for all the characters and most effects (hitsparks, misc particle effects, etc), but the backgrounds are completely done in 3D. They use a nice mix of polygonal geometry and 2D assets (mostly for characters in the background), but the overall look gels really nicely with the characters and makes for much better depth in the backgrounds than you'd tend to get with pure 2D backgrounds, even with lots of parallax scrolling.

(Other 2D fighters that used the same technique to varying degrees of success include Capcom vs SNK 2, Marvel vs Capcom 2, King of Fighters 94 Re-Bout and The Rumble Fish)

Another example that quickly comes to mind is Strider Hiryu 2. It doesn't look quite as impressive on accounts of running on more primitive hardware, of course, but it still looks nice and I think the use of 3D serves the game well.



Generally speaking, I think 3D can be used to great effect in 2D games, if done tastefully and with some thought behind it. Basically as long as the camera remains at a fairly static angle relative to the sprites I think 3D can add a sense of depth to something you would expect to look kind of flat, whereas 2D elements in a fully 3D environment kind of look flat where you expect three-dimensionality. Regardless of how you do it though, I think a key factor is to make sure that the 2D and 3D elements simply fit together as well as possible so that neither looks out of place compared to the other. I think the Pokemon and Prinny games mentioned earlier pull this off quite well, judging by those screens, whereas... I dunno, Mario Kart 64 perhaps doesn't manage to do it quite as well. Strider Hiryu 2 arguably has a more visible discrepancy between the 2D and 3D elements, but I dunno, personally I think it works quite well anyhow.

I guess it's a matter of taste; I like 2D art, particularly well made pixel art (and it doesn't get much better than Capcom in the late 90's), so in some cases it doesn't bother me if the 2D elements call a certain amount of attention to themselves.