Prices are a little bit higher than face value (but let's see you get tickets directly from Barcelona's, Arsenal's or the other major European football teams websites for the big matches).
Their customer service is the best in the business (always answer on the phone and helpful with every questions).
And the delivery of the tickets is always no time including good seats (one time I also got a free upgrade!).
There are many secondary ticket websites online – a lot of brokers or suppliers – But Football Ticket Net is really the best.