I really love Dairanger. It's one of my favorites.
A lot of the "weaknesses" mentioned for the show I don't really think are that major at all. The plot twist at the end doesn't ruin what the whole show was going for. And I love how the show manages to maintain an air of mystery without giving an answer to every single thing. I myself loved the finale a lot. I'll agree that the plot twist is a bit strange, but I think it's far from anything offensive. Definitely not on the same level as Ryuki and Faiz's endings.
I don't think Kazu is as useless as many claim him to be. Yeah, he gets the least focus and definitely deserved more. But overall, I think he was a very enjoyable character and the actor did a superb job imo. And while his own story arc doesn't stand out as much as the others, at least the show didn't forget Kazu existed. That's what I love about Dairanger. Even when one character is the focus of one ep, it doesn't forget that there are other characters in the show. That's why Kazu still feels like a strong character to me.
I really love Kou. Yeah, he's a pervert during his first 3 eps, but I thought that was pretty funny. And yeah, he does get upset quite a bit during his first 5 eps, but I think it's pretty understandable. He loses his mother and just wishes he had the love of a parent. It's a much better reason compared to those brats from Black, Bioman, and Zyuranger who get upset when they don't get a toy that they want.
I don't think "Sixth Ranger Syndrome" would describe Kou. Kou wasn't intended to be a full fledged character like the other five were. Was still a major character, but I don't think he was meant to get as much spotlight compared to how Sixth Rangers are executed in the last 5 years.
There's really too much to say about why I love Dairanger. I think a lot of people on this thread already said most of it. If there's one major weakness that Dairanger has imo, it's the Gorma monster designs. And this is due to how low budget they look. Rather disappointing compared to the designs of Changeman's Gozma and Maskman's Tube. But then again, it kinda gives it it's own unique charm. However one looks at it.