I think its a pretty darned great book. They managed to update it (attracting new players) without making it any less of a 'thinking mans army'(therefore not alienating its veteran audience). Not saying that everything in the book is super viable 100% of the time, but given the right local meta I'm sure everything would have a use (Even Banshees...:P)
Played my first game with new eldar, really enjoyed my game, and even the banshees were usefull, really funny when the banshee exarch disarmed Azreal, just took my 5th edition army with no wraith knight or flyer (I have them but wanted a baseline) and it was fun, competitive and fluffy, tried all the troop types
Found them all usefull and fairly tough, those warlock powers are really usefull, and eldrad was casting 5-6 warp charges a turn with his special rule, swooping hawks are actually worth leaving in the table to shoot with now (not that you get a choice anymore) and the run/shoot shoot/run rule seems meh on paper but is actually really usefull even if I did forget it half the time. Of all the codexes done in 6th so far this is the oldest and it still feels like the same army I've always had, well done gw! Next game lets see how that flyer and wraith knight fair :)
I've tried all the units over 3 games and I have to say this book is fantastic! I like what they did with the aspect warriors. Spiritseer combos are amazing!!