For some reason Amazon puts reviews of any edition of a given Shakespeare play on each edition's webpage. So, if you are wondering why to buy the Folger over the Cambridge or the Cambridge over the Arden, or just to spend a buck on the Dover Thrift Edition, you have to wade through dozens or hundreds of reviews of all the other editions. I have no idea why Amazon does this, as many people will have very particular interests, and various editions will serve those interests differently. It's maddening. Amazon should keep its Arden reviews on the Arden page, Dover on the Dover page, and so on. What gives???
Anyway, it appears that Arden's Third Series of R&J is unavailable, or perhaps not yet out. If it is available when you read this and you are looking for a first-rate scholarly edition, I'd buy that one -- although I confess I've personally never seen it. But the Third Series of the Ardens, and I have read many, are really first-rate.
The Second Series of the Ardens vary. I'd put this one in the middle. It's quite a bit more thorough than what you would get from, say, the Signet editions (or Dover) but maybe a wee bit out of date and, like most Arden Second Series editions, extremely concerned with editorial conundrums and less concerned with exegesis. But there's a lot of that in this edition, and I am quite satisfied with it. I will, however, buy the Third Series when I can.
One other point I always make about the Ardens: of all the various editions, these are the sturdiest, by far. They are extremely well bound, with sturdy bindings and paper, and will hold up to years and years of abuse and underlining and spilled coffee. Honestly, I prefer them for that reason alone.
Happy reading to you all!