What is Iceland?
Iceland are a supermarket mainly catering to frozen food, as their name would suggest.

What can you buy at Iceland?
All sorts of frozen food - ready meals, pizzas, chips, burgers etc.
A small selection of vegetables, fruit and fresh meat (nowhere near as much choice as other supermarkets).
Dairy products - milk, cheese, yoghurts etc.
Confectionary
Drinks
Cleaning products
Some brances of Iceland also sell fridges and freezers although there doesn't seem to be much choice and my local branch has stopped selling them all together in the last few weeks.

Price:
Iceland pride themselves on giving the customer value for money and in many cases I would have to say that they achieve this - 4 pints of milk at Iceland is just £1 (other supermarkets are around the £1.56 mark) and 3 packets of supernoodles are also £1 (currently £1.60 in tesco).
Of course some items are priced roughly the same as in the other supermarkets but some of the prices such as listed above are too good to ignore if you're trying to save money.

Quality:
I've purchased several Iceland own brand products and have to say I've been very happy with the quality of them, definately worth the price you pay. Iceland also sell branded products so these are somewhat of a known quantity.

The store:
At the store near me they've arranged the freezers so that the only way to get to the tills is to walk around the entire shop, I imagine they have done this as it means you are forced to pass more items on your walk to the tills and will hopefully buy more. I don't think all brnaches of Iceland are arranged in this way though.
Like other supermarkets everything is arranged in labelled sections eg. the chicken freezers, pizza freezer, chinese takeaway freezer etc.

Staff:
I rarely see staff wondering around the shop floor and the tills are never fully manned (never more than half of the tills seem to have someone at them) but this usually doesn't matter as I've never found Iceland to be busy and the queues are usually short and quick moving.
Staff tend to be quite friendly.