You can find great bargains at Filene's Basement, but you have to search for them. Unless you get there right when they open, on the morning after they've cleaned or restocked, expect to find the place disorganized and messy. Bargain hunters, apparently, cannot be bothered to hang clothes back up or put that sweater back on the table they found it on. Maybe doing so might cause them to miss some huge bargain?
That said, if you are willing to sort through the mess, you can find some very nice clothing at significant discounts, especially if you are willing to buy offseason. I found some great sweaters last spring that would normally have run me $40-$75 dollars, which I was able to pick up for less than $20 each.
Don't bother asking a salesperson for help finding an item, either. He or she may be able to point you in the direction of the dress section or the men's area, but because of the constant moving of the merchandise, probably can't get more specific than that.