[Suzu]

I think it's a bit hard to go by halves, because most seasons have certain arcs and some have points in the halves that are better or worse than the rest of the show.

For example, Shinkenger and Toqger start out pretty strong, than have a little stretched period around the middle (which happens pretty often in Kobayashi's shows) and then improve again near the end.
Then we have shows like Magiranger and Goseigers which have three phases. Magiranger starts somewhat slow and improves noteably with each phase, while Goseiger takes a bit longer and really starts improving around the end of the second arc and then suddenly shoots up like a rocket in the last arc.
We also have shows that stay at about the same level, such as Gekiranger or Go-Onger...

It usually really depends on who is writing it, so generally, each episode can be a hit or a miss at any time. I had that with Megaranger. While the second half was much stronger than the first, there where still some excellent as well as some terrible episodes in both halves.