If EVF is used, It must
1) have no lag, shot to shot
2) usable under low light conditions, comparable to OVF
3) have low power consumption
4) be able to resolve fine details
Personally I'm those that still prefer an OVF, mainly becos its simple, it works, efficient(dont consume power), its clarity, ruggedness and reliability. Elegant solution to a problem, engineering at its best.