traffic – go several times, at different times of day, before you view, to check the traffic levels
neighbours & noise; is there an airport nearby?
nearby park/offie/pub combination – if there is one, that's where the scrotes will hang out. if it has a "no ball games" sign you can guarantee that's exactly what they'll do. Usually involving slamming a ball against a wall as hard and as frequently as possible for as long as possible
dogs
if all that doesn't put you off, check which way is south, and is it in the shade of a great leylandii hedge and/or skyscraper
if you have kids, where's the nearest school – preferably within "leave the mum-wagon at home" distance
Play around with car & home insurance quotes based on your current & proposed new postcode – if either goes up significantly, why?
Check http://www.upmystreet.com to see what they think of the area
how near is the nearest newsagent/convenience shop/post office/pub/takeaway etc? You don't want to have to get in the car just to fetch a pint of milk, do you?