Try to ignore the noise levels and how scary the bigger children look when they're running around. Any school can easily look too vigorous if your frame of reference is the cosier world of toddlers.
But look at the bigger children: what do you think of the way they speak? How they interact with teachers, the head, their peers and you as a visitor? What is behaviour like in the classroom? Does it have a purposeful buzz, or is it inappropriately random?
Look at the work displayed: do displays look recent or is it still bonfire night in February?
Even if the buildings are tatty, are they well kempt and is equipment tidy? Is there any litter or clutter? Are the loos clean and is there enough soap and loo paper?
What clubs and activities are there? Are they receptive to setting up new ones if your DC has a passion which is not currently catered for? (Not so much about getting XYZ actually provided, more an indication of attitude to new ideas and willingness to give things a go)
What are the opportunities for art, music and drama? What plays and concerts have taken place in the previous 6 months? What trips out have happened?
How does the school prefer to communicate with parents? Is there a PTA and what does it do? Are there any ongoing charitable or community projects?
But in the end, it's all gut feeling, and whether you want your child to become like the children you see who are in yr6.