Nothing. But 90's Sentai are 90's Sentai, 80's Sentai are 80's Sentai and today's Sentai are todays Sentai. I'm glad that every decade is different, because it's more fun that way.

Sometimes i think how would be the sentais in the future.I mean they will be different than today ?

Not that I'm saying its a bad thing but the execution can sometimes be bad. Some older shows have great episodes, while newer ones don't. They both have episodes that slow down a lot.

The thing about older sentai is that they stay in the same trope for so long and fall into so many clichés. Makes the show boring to me when I know what's going to happen next.

That's actually my primary problem with older series.

What about the newest shows ? you don't think they don't have cliches too ?

Same here. Sun Vulcan felt pretty repetitive most of the time.

They do, but they generally have a greater variety of themes (thanks to the possibility of making more fantasy-oriented stories too) and generally have some more fleshed characters.

70's, 80's, and 90's sentai stuck to a pretty rigid format with the story arcs, the rangers, and the villains. Each show had a villain that would betray the main villain or have a moment of redemption, there was always a ranger with something from their past they tried to keep hidden, the ranger that was overly care-free and it annoyed the "by the books" ranger; that stuff gets old when you see that for about 20 straight years. The newer seasons do have more variety in the characters and have added to the tropes while getting rid of others.

No era of sentai is perfect, but each offers something that is better than the previous. Like Suzu said, it is good to see the show evolve. Go-Busters took the old school/80's and 90's approach to a season and it is considered an overall failure. I think that is all the proof that Toei needed to veto the idea of making the show like they use to two decades ago.

I didn't see that is looks much more reboot than a old school stuff.I think Toqger have more relation with old school stuff.Toei bring back the old formation of 5/6 members back no extra rangers crap.

6 members isn't even "old", considering that the first 6th ranger appeared in Zyuranger- which is season 16.
And how are extra rangers crap? Some of them are pretty cool, like those in Deka- or Magiranger.

Extra members have even been around since old school sentai. Remember big one?