Unless you know the layout, it's not easy to use a...

Unless you know the layout, it's not easy to use as a meet-up destination - too many avenues to get lost in. However as a departure point, I really like it.
The food hall is great and there are some excellent coffee houses. The toilets are generally clean but queues are common.
A tip; be crystal clear which part of the station you want, it's very easy to "lose" the platforms or end up at King's Cross. If you're not sure - ask.