We all love BB and would probably watch it even if the cast was made up of twelve Ronnies (ok...maybe that would be the one scenario that goes too far). But there's plenty to complain about, or maybe a nicer way of putting it is that there's room for improvement.
1. Stop casting "types" and start casting people
The later seasons are dominated by fame whores (i.e. aspiring models/actors/professional wrestlers) and HGs specially recruited by producers to fill certain roles or to basically "recast" memorable HGs. It seems like as a result, the casts in these later seasons have become more and more full of vile people. It's fun to have villainous players like Dr. Will or Danielle who are fun to watch, but people like Jessie don't even register on the "love to hate" scale. I just hate to watch them.
Maybe it's naive, but I do believe that you can have a successful, outstanding season of BB if you have a diverse cast of genuine people and/or fans of the game. As long as they're interesting, that's all it takes (just look at BB2/BB3). You don't have to force fit them into types--and when you cast types you'll have people auditioning trying to fill them, and when they end up on the show, they're not who they said they were.
2. The live feeds need to be vastly improved
And I don't care if they have to do more annoying product placement on the episodes to afford it.
I will admit that the flashback feature was a major step forward. Yet frequently all four feeds are on the same event, or at best we see two events across four feeds. And don't get me started on the blocking. The endurance comps are a prime reason to get the feeds, but not when they block the first 50 minutes and people have already dropped out.
It's optimistic to think they'd even improve those aspects, but a dream goal would be for them to show at least some DR sessions on the feeds. Fine, some involve production and we can't see them, but it would be nice to see what they're really thinking and strategizing about in their other sessions. Or maybe just have a time when the HGs can go in the DR and vent to the camera without interacting with a member of production and we can watch that.
3. Twist the game rather than the HGs
This goes back to casting types. Sure, ideas like cliques, couples, and secret partners can change the game slightly, but it's usually not in an interesting way and it just results in poor casting choices. And what really matters for BB is having a quality cast.
Instead they should try to twist the game itself and even the non aspects of the game. Make PoV a mystery each week: they could play for the original PoV, the golden PoV, or the diamond PoV but not know which one until they win it. Maybe even give America a single vote in evictions but not be represented by a player inside the house (though that might work out poorly). Implement a version of the coup d'etat that can be revealed to the other HGs without them losing it. Create another power (but it wouldn't be every week like veto is) where the comp winner can put up a third nominee even if the power holder is a nominee him/herself.
4. Add more to the BB experience not directly about the game
Remember the dance marathon during BB1? I'm talking about things like that, only better, that add to the experience for the live feeds viewers and also the "social experiment" aspect of BB. All they seem to focus on is game anymore, and as fun as that is, there's more to BB than that. Make them fight over what food they can afford to get again. Create conflict by influencing non-game aspects of the HGs' experience. It will probably only create more drama in the game itself which can only be a good thing.