A lot of folks seem to be gushing over AU. While I think AU is definitely deserving of said gushing... I don't think people are giving enough credit to the game that spawned it: DnD.
I have both 3.5 and AU. I like both of them. They're both good, but in different ways. Personally, I like the fact that I now have such a diversity of good material to pick over.
I only got into 3e DnD in the last 9 months. I found it to be very good. I have always enjoyed playing what are now the traditional DnD archetypes. I'm pretty sure I'll never get tired of playing them.
That said, AU offers some new and alien archetypes. It is important to note that these archetypes are alien because I hear these nagging questions from myself and others... "Well, how do I play a [insert traditional DnD archetype here] in AU?" There are very few direct analogs between DnD and AU. Does that mean that one or the other is better? No, but they are different. Does that mean that one is more flavorful than the other? No, they're just different.
Now after all of that... My group is converting to AU, but we're tacking the Psionics Handbook to it. Why? call us kooky, but we like the PsiHB... and it's an integral part of our current campaign.
My character is 3.5 Ranger2/PsiWar2. There are no direct correlates for Ranger in AU. This made my conversion difficult, but not impossible. Based on the history of my character I realized that the following progression made sense, but also gave him enough Ranger cred that it might actually work...
Level 1 = Unfettered
Level 2 = Wolf Totem Warrior
Level 3 & 4 = Psychic Warrior
It's a bit of an odd progression, but it made sense for the character. Do the first two levels really make a Ranger? Not exactly, but they do make a very interesting Ranger-like character. I'm happy with the results.
I'll found out this Sunday whether I like playing this new "Ranger" better than my old Ranger. Either way, I like the archetypes from both systems.
--sam
EDIT: grammar