Top 10 Style Changes that Resulted in Bad Albums

ClemofNazareth wrote: Unfortunate lineup changes and shift to a more pop-structured song format for Jefferson Airplane on 'Bark'. Abandoning strings for synthesizers (The Moody Blues on 'Octave' and ELO with 'Discovery'). Wishbone Ash trying to do country (poorly) on 'Locked In'.

you know, i happen to really dig the Locked In album, though i realise that i am in the minority on that (i understand even the band themselves have bad memories of that album)

Best changes:

King Crimson: Heavy fusion (Larks)  to new wave (Discipline)
Donovan: Bob Dylan-styled folk to psychedelia
The Beatles: Everything.

Worst changes:

The Byrds: Psychedelia to country. Not necessarily the change itself - the Byrds were capable of doing good country - but their first full attempt at a country album, Sweetheart Of The Rodeo, was kind of mediocre, the last time I heard it. 

Frank Zappa: A good chunk of the Flo and Eddie era. Filmore was boring and the 200 Motels soundtrack was useless without the film. His later works like Apostrophe and Sheik Yerbouti were much more focused.

ELP had already changed before the Love Beach album by doing solo music on Works and largely abandoning the synthesiser in favour of orchestration. Works Vol One was a decent album though. The most jarring change for me was Genesis and Abacab. I hated that album and still feel much the same all these years later.