Is Assassins creed series always bad or turn bad?

Always middling. The premise behind the OG trilogy was interesting, but then they just went off the rails. Gameplay has improved, but not enough to make the franchise drastically better imo.

The most interesting thing about the series is that it has influenced the modern day open world formula.😮

This.

I think if you accept that the AC games have always been terrible stealth games and the best ones are the more action-oriented ones, there is fun to be had with them.

I think its been a pretty inconsistent series for its duration though. I think AC4 and Valhalla are the ones I enjoyed most.

I got some enjoyment out of Brotherhood and Origins. I guess the parkour in the original AC was novel for a short time, but honestly it was a pretty terrible game.

the rest I have not liked much at all, or didn't play. I didn't play Unity or Syndicate which some people seem to think are the best ones so IDK.

I also have never actually finished an AC game. I think I got pretty close with Black Flag and Brotherhood. most of them I don't even get close to finishing.

Turn bad

AC1 and AC2 were great. The rest is useless garbage.

AC games have a lot of repetetivness.

Yes, it's bad, but only AC1 (very dated), Unity (was buggy mess), Origins (I did not like direction), Valhalla (again, a buggy mess). The rest, I haven't played. Overall, I'd say they are solid 7.