[BBDodge]

Looking at the Wikipedia pages for the early shows:

BB1 - no twists at all

BB2 - only twist was the public voting in an extra housemate from a choice of 3. But the housemates were told on Day 1 that a new housemate would enter after the 1st eviction.

BB3 - the first nomination twist when the viewers put 2 up for eviction and the Housemates chose which one to keep (unwittingly creating the Jade Goody phenomenon). Then later we had the rich/poor divide. We also had the first letters from home with 2 housemates chosen to receive them in return for being put up for eviction.

BB4 - This was where the twists gathered momentum. The Day 1 nomination twist sealed Anouska's fate. We had Cameron jetting off to Africa with Gaetano guesting here. We had the first double eviction which saw Fed & Jon going but they then felt they had to bring Jon back to liven up the show, even though he couldn't win. Bit of a mess.

Since then the gloves were off. We've had secret rooms, fake evictions, face-to-face noms, friends and family noms, returning housemates who could win, multiple evictions, nominations reversed so those with the least noms faced the vote, killer noms, immunity for a single eviction or all the way to the final, housemates' partners being thrown in, couples in the house from the start, fake housemates, moles, etc. etc.

It became a rarity to have a week when the housemates just nominated in secret and those with the most votes faced the public vote for a single eviction with no return.