I'm not on about the effects. I'm on about the production design, direction, cinematography et al. The Sontaran 2-parter in S4 is a total assault on the eyes. So much purple
Seriously S4 is barely different for all those things than Who is currently - the sixties stuff is very different. British TV was still shot as if it was theatre being filmed at that point.
It's my favourite era of Who but it looks like a different world in terms of pacing, direction etc - some of the direction is clumsy (Richard Martin) to a point which would never be allowed these days then you have crew members popping up in shot.
It's a shame but the vast majority of people struggle to watch it because it is such a different visual experience - even many Who fans won't go near the sixties stuff.