PHB's my favourite - a work of art. There are a few flaws - mostly the Cleric class being made too powerful as a way to try to get people to play them - but the basic d20 system is a brilliant update to bring D&D into the 21st century. I like the miniatures-based combat rules, the tactical flavour is nice for tabletop play. Not so good for mini-less play, though. 5*
DMG is functional, not bad at all, but somewhat uninspired. And I disagree with Monte's high-magic assumptions in world creation. I do quite like the magic item creation rules. The lack of a proper system to assign monster CRs is very annoying though. The NPC tables are nice, as are the NPC classes. 4*
MM is poor, IMO, without nearly enough of the classic monsters (such as Humans!), too many silly new monsters, no wilderness encounter tables (though those could/should have been in DMG).
Most of what's wrong with 3e core rules IMO comes down to the monsters. I rated it 3* in my review, but on reflection that was over-generous at the full price ($30) - for the $20 I paid it was reasonable.
Everything else is unnecessary to have, although I have a few (MoP, PSiH etc).