I think the other problem is concept..
We were told by both the contestants and the psychologists that BB2 was designed to produce a "family" group where there were alternate candidates for each role (mother, father, entertainer, daughter) - the entertainers were strong (brian) and provided entertainment and the daughter provide romance (helen)
BB3's concept was never revealed, but the history of the contestants all displayed some leadership role or the person was pretty quickly seen as an alpha male/female by the other housemates/fans because of their personality, educational ahievement, looks or physique (think of the males then note that, Adele was school captain, Kate was games captain at school, Jade was reportedly the school gang leader, Sunita had obviously excelled academically and Allison had been a holiday rep leading a group of similarly aged people on holiday)
Arguably that was the idea - BB2 produced an obvious leader and mate - BB3 would produce competition between 12 people who would accept no leader. They then picked people who had flaws that were noticeable as well as meeting the potential leader criteria (for example: overenthusiastic Allison, plotting (but incompetent ) Adele, controlled Sunita, miserable Sandy, idle Spencer, Alex (think of the " why am I here ?" speeches) Jonny and the ultimate - posh but dim Tim. They then threw in Jade and the divide and let the pot boil. The contestant who emerged at the end actually having best survived and enjoyed the process won.
BB4 responded to the critics attack on BB3 by removing competition and any obviously flawed people who might become media targets like Adele, Jade or Tim. . I think with hindsight that you could describe most of the people in BB4 as nice, normal and relatively uncompetitive. I think they were also picked because they had smaller flaws that would create some tension over the series but which would not produce Jade, Adele, Jonny or Tim. For example think Federico and the tasks, steph and her jealousy of Nush, Ray and his temper, Cameron and his attitudes, Sissy and the tears, Anoushka and the noise. Even the loveable blonde beauty Nush could be annoying, self centered and giggly. . I think BB4 was designed to let these problems simmer and the one with a story would emerge as winner (even if Cameron's story was invented for him.)
BB4 failed because the simmering was pretty invisible and the housemates were too controlled. It also failed because the housemates took the obvious action and removed the oddest people as soon as they could. Unlike BB2 where the family removed the outsiders or BB3 where the competitors formed 2 groups , in BB4 the only logic of nominations was to maintain peace and quiet and nice scenary. The boys removed the annoying females and left themselves with the house maid and the house beauty. BB4 also failed because as there were no sides, no bad people or good ones and similar, slightly annoying, people, the public didn't really care who won.
I don't know what the concept for BB5 should be but some obvious ideas would be:
Competive people are better TV than non-competitive.
Reward rooms do not work - putting the losers in a sin bin for the day might be better.
A house divided into groups produces more interaction in the group and between it and other groups
Something has to be done to make sure the house does not divide boy-girl again - boys will vote out girls and girls will join them doing it .
You need an winner who looks like a winner. BB3 had 4 (Spencer, alex, Jonny, Kate) BB4 had no one.