Great things about Visiting Seoul - why I would recommend a visit:
very different to UK/Europe
Great variety of things to do and all tastes catered for
language not really an issue, you can get around easy enough without Korean as your language
Very large spacious city, modern, clean and well organised
Cake shops - best cakes I have eaten
Views around the city, parks, water front walks, nice for cycling, good cycle hire facilities
street cleaning - not seen rubbish, lots of people clearing up there own mess

Parka's - loads of these being worn, very trendy
no graffiti
feels extremely safe, even when busy
Busy night life, city always alive, easy to get anything
Olympic Park, great days visit
main Temple and lots of other temples to see
Lots of good shops
Train & Subway system - fast, clean, regular, very tidy and easy to navigate, No free newspapers cluttering up trains, seats for disabled, older people, pregnant women - no one sits here unless they are one of these groups. trains spacious
Lots of great coffee houses
Temples and museums, really good, and interesting,
People passive polite, smartly dressed and picking up their rubbish
Food - lots of choice, variety
Seoul Zoo - Really large, well laid out, great cable car ride to zoo, also you can visit a super theme park at same location.
N-Seoul Tower - Good place to visit, views are fantastic, but go on a clear day
Mountains around Seoul

Differences/strange things:
Large glasses, wearing glasses with no lenses
Riding motorbikes - not wearing helmets, and riding motorbikes on pedestrian crossings and down paths
spitting in public
bugs for sale in streets as snack food, live food in streets to eat,