Have the first four. Use Noble, have used Assassin for NPCs. I'd use Exorcist if I used vancian magic in my main campaign, I think it's a nice concept. When I start up my modified greyhawk game again, I probably will.
Of the next batch, I will get them all... I will probably use Knight right off the bat, and depending on exactly how the Explorer turns out, I may or may not use that, but I will probably harvest ideas from it. I'll use Hedge Wizard as soon as my greyhawk game gets going again; it's a concept I've wanted to see done in D20 for a while without it being purely an NPC class. I don't know that I'll have a specific use for artificer, but again, it's something I've wanted to see a good treatment of in D20 terms as a core class, not a prestiege class.
As for mongoose in general... *shrug* Overall, I rather like them. I'm a huge fan of their encyclopedia divine/arcane. Huge fan. Their slayers guides are neat... I don't go out of my way to get them all, but I have a few that interest me, and I've been happy enough with the ones I have. I love the concept of the quint books, though I only have a couple of them thus far. I liked their Crusades of Valour book, to be honest, though it didn't get the best reviews.
Some of their other products are great, though. Slaine comes to mind. Slaine is, quite simply, excelent.