My comment which is long enough to preserve is:
My impression is that Soc/Plat is reasonably good on the negatives: using questions to expose flaws in the opponents reasoning and ideas. But poor when attempting to put forward his own ideas as positives. Which ends up making the questioning seem cheap: it turns out that exposing at least a minor flaw in someone else's ideas is really not that hard; building something able to withstand close questions is difficult.I find I've touched on this before; Justice and Injustice.
And to be sort-of fair it is the questioning that he is remembered for; no-one actually remembers the city-state-building in the Republic (and if they do remember it, they hate it).
There is also (sorry, I'm getting carried away, stop me when you're bored) possibly a very big philosophical error in all this, if you believe Popper's analysis. It's also quite subtle so I may get it wrong. It's in TOSAIE vol 1 I think. His point is that definitions - like "what is a puppy?" - in the hands of Plato turns into the Ideal Form of the Puppy, in order to explain how we all see young dogs and all these disparate objects are recognised as a puppy. Popper asserts that instead that it should be read in reverse, as a description. This does away with any need for Ideals, but it also implies that focussing on the meaning of a word - like "the Good" - becomes as pointless as focussing on the True Meaning of the word Puppy.