A lot of the best... and worst... bands out there have a way of progressing or evolving.
It's not that they shift styles according to seasons (though not all bands that did that are awful- Alice cooper handled it well), but that they actually gradually change.

I find this to be common in death metal and black metal bands... probably because they just start off focusing on noise and gradually inject musical talent... until they end up with something interesting.
The band Death can be seen in this light, but not very extreme... They were still a death metal band at their disbanding, albeit one with amazing musical ability.

But there are some bands that gradually shift to a completely different genre.
And if you listen to their first album back to back with the last, you would think it's two different bands.
But unlike, say, Metallica... who changed overnight, it's gradual over the course of many albums. There's a consistent pattern.

Amorphis would be an example:
vs.

I think that kind of thing works well until the band goes stagnant... which Amorphis has probably reached that point, as have most of the oher bands fitting the pattern.

Other bands resembling this kind of a pattern would be Anathema, Covenant/Kovenant, Paradise Lost, and Ministry.

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"Man lives in the sunlit world of that which he believes to be reality. But unseen by most is an underworld, a place that is just as real... but not as brightly lit... A DARK SIDE!"
-opening from Tales From the Darkside