I've been in here a few times, and always been served very quickly (never seen a queue). There's always plenty of places to sit, it's a medium sized place and they keep it very clean.
Subway's sub of the day deal is great for £1.99 you get a nice big 6 sub. They do a number of promotions too, I've won plenty of drinks, cookies and subs that way!
Their coffee and choice of soft drinks is pretty average. I like their choice of breads and the herby cheesy ones my favourite. Also they have a good choice of sauces, and I really like the sweet onion one.
I only recently found out that there's is a Subway hidden inside the cascades. Take the lift up to it (opposite T K Maxx). As it is a bit hidden out of the way it tends not to be very busy which I really like as you get served quickly and there's always plenty of places to sit. The food and drinks are pretty good and their sub of the day is good value.