I don't think you can really compare the two sequences of the Amber novels, as they are two very different types of stories. If you do, the second sequence suffers greatly in comparison, which is unfortunate, I think.
I really enjoyed both, but the first 5 books are definitely more epic in scope than the second, and less bound by technicalities. If anything, I think the two sequences are very good examples of writing to a character's strengths- Corwin, the hero of the first series, is a poetic, somewhat jaded, epic figure- he's not really a hero, but rather someone who ends up in a situation beyond his initial comprehension, but who bulls through it and manages to come out on top by sheer grit and wit as much as ability. His descriptions are more colorful and fantastic than are those of his son, which is perfectly in keeping with the character as revealed to us throughout the course of the series. He is the Bill Shakespeare of the Amber universe.
Conversely, his son, Merlin, is not nearly as eloquent as Corwin. He is far, far younger, and he is both a student of magic and an engineer- and that last portion is sort of his viewpoint on life. He wants to understand the underpinnings of things, how they work, the logic behind them. As a result, the viewpoint that Merlin reveals is far more technical and involved than Corwin's musings and observations. Merlin is deciphering the workings of the Amber cosmos, as are the readers, through him. Like his father, however, he manages to bull through his troubles through wit and talent- not a little of that talent his own magical strengths. Unlike Corwin, Merlin is not adept enough to do things solo, and must rely much more heavily on companions (many of whom have shifting agendas, perhaps even moreso than Corwin's relatives in the first series) as well as blind luck. He may not be entirely successful (at least, some think so) but I think it's pretty evident that the potential to live up to his father's example is there.
In any case, I recommend that you do read them, as well as the short stories that follow if you can find them (and, for anyone who is interested, the book "Manna from Heaven" coming September 30 from Fantastic Book Club, finally collects them all together). Like I said, viewed together, I think the second series (while good) pales in comparison to the first, but if you view them separately, and as character studies of two different types of people, I think both are very strong and interesting storylines.
On the other hand, unless you are a completist, I'd recommend against John Betancourt's "Dawn of Amber". I picked this up in paperback recently, and was underwhelmed. There were some interesting ideas in there, and he works with the Amber cosmology fairly decently, not invalidating or contradicting any of Zelazny's work, but the characters are dull and uninteresting, and some of them just seem off- Dworkin, for one (admittedly, this is set thousands of years or so in the past), and Oberon (the main character) for another. Again, I realize this is a young Oberon (only 24 or so), and much of his development will presumably take place in the course of this series, but he still doesn't strike me as particularly interesting or strong. (He weeps at least once in the book, as does Dworkin... c'mon, this is *Oberon* fer chrissakes!). Unlike the Zelazny works, at least thus far, Oberon has no qualities or personality that can be derived from the first person viewpoint that make him unique... if you changed his name to Caine, or Benedict, or Joe Blow, you'd get the same sense of attachment to the character.
Anyway, hope this helps.
