I am another who prefers T3 to T4, they just got so much wrong with T4, the T-600's they gave us would have never passed as infiltration units even with human skin, never rubber, they were for too big.
In T1, Kyle says "you stay down by day, but at night you can move around, you still have to be careful though as HK's use infra-red."
The in T4, young Kyle says the complete opposite! Also, I liked Worthington's character in T4, but he didnt really have much of a purpose, and JC's role was written pretty poorly. McG should have been the last person to direct it. At least T3 didnt mess with the mythology, and with its ending, actually advanced the story a bit.
I just dont know were they could take a T5, I am a huge Terminator fan, especially of the first 2, but I think they messed the last movie a lot so not sure were they could go. The future provided in T4 wasnt what was envisioned in the first 3 movies at all, so a lot of repairing would need to be done and we would probably get another re-cast for JC which would be ridiculous.