So, I've done a lot of encodes of Toku DVDs over the last couple years. If you've watched them, you'll probably have noticed that some of them look better than others. This is due to three main things: the way the show was made to begin with, the masters Toei used when making the DVDs, and the type of DVDs I have access to.
There are five main type of ways Toei's shot and edited their Toku shows.
Film-shot and edited: Almost the entire show is shot and edited on film. There are video effects, but they were still output to film. The entire show can be rescanned to a nice, crisp, progressive ~24fps master. THis was used for all of Showa Rider, all of Metal Heroes, and all of Sentai from Goranger through Carranger 5.
The second type is where the show is shot in 30i (30 interlaced frames per second, so 60 fields per second). This was used for Kamen Rider from Kuuga through Hibiki, with Kuuga shot in HD and edited in letterboxed SD, Agito-Blade shot and edited in SD, and Hibiki shot and edited in HD.
The third is where the show was shot on film, but edited digitally at 30fps. Most source content is progressive 24fps, but the way it's edited means it finished product isn't.. This was used for Gaoranger through Majiranger.
The fourth is where the footage was shot at 24fps (either film, or digitally), and edited digitally in progressive form. The final product is also mostly 24 progressive frames per second.
The fifth way, used for Carranger 6-Timeranger, is similar to the first, but some of the editing (mostly the OP was done on tape, meaning the finished episode is on tape. And this is pre-2001 Toei, so the transfer looks like ass.
Big factor number 2: the masters used on the DVDs: For series prior to Gaoranger and Agito, the masters used for airing the show were analog tape. These were also used for the DVDs of earlier series. How clean these masters are varies from series to series. From Car episode 6 to the end of Timeranger, there are combed and blended frames all over the place. Older series don't have that problem, but they tend to have a lot of noise. And Kuuga? It's letterboxed to fit in 4:3.
Series with "bad" masters used for DVD are Goranger, Jetman, Carranger (ep 6) through Timeranger, Gavan, Sharivan and Shaider, Kamen Rider X, Amazon, Stronger, and Kuuga.
Later releases were mostly rescanned. These look great. And starting with Agito and Gaoranger, the masters were made with DVD release in mind. They also look great.
Big factor 3: the DVDs we have access to. Most show volumes are released on DVD9. These are dual layer discs., with 9ish GB capacity. However, may isos on the internet were made bu recompressing the DVD9s to fit on DVD5, single layer discs with 5ish GB capacity. No matter what, you lose a lot or detail from this re-encoding. Some series fare better than others. Rescanned series and ones digitally edited at 24fps come out OKish, but unrescanned series and interlaced series suffer the most and are Block City.
So, what does this mean? It means there are some shows that really, really need a DVD9 source to not look like complete shit, while others need them to not look kinda shitty. And recompressed DVD5s are never going to look great.