Despite Gringott's being down, I personally had a great time in Diagon Alley. Ate dinner in the Leaky Cauldron, bought a wand (and used it successfully), bought other stuff, and got ice cream (earl grey and lavender is wonderful). And I gaped at the dragon when she (She is a she, right?) did her thing. Will post some pics when I can tomorrow.
The area itself blew me away. Talk about your immersive experience!