Well I for one use lots of Mongoose products in my games, and there are some really excellent books out from them.
I actually use I would say at least one or two things for definite in my own home build campaign setting from most of the books.
also to those of you who would judge the company based on one or two books you may have seen, you should realise that Mongoose has many writers, and among them some real gems. Sam Witt, August Hahn, Ian Sturrock and Matthew Sprange himself among my favourites. I would also add J Miller as a noteworthy as his EA: Familiars, Crouching Monkey, Hidden Toad was a fantastic book and Robert J Schwalb has my eternal gratitudes for the fantastic job he did with Quintessential Witch.
those doubters among you should also note that its easy to judge, but what other company puts out as much as regularly as Mongoose does? I'll tell you noone thats who.
Mongoose Publishing
Green Ronin
Bastion Press
are my three favourite companies outside of Wizards and they ALL produce quality books.
This is not to say every Mongoose book is wonderful, not at all. But as with any book from ANY company every book has its high and low points, but no book is iredeemably broken by Mongoose or anyone else.