It appears that Amazon.com has mistakenly listed Avengers Assemble Vol. 1 (http://www.amazon.com/o/ASIN/0785115730) and Avengers Assemble Vol. 2 (http://www.amazon.com/o/ASIN/0785117733) as the same product.
Avengers Assemble Vol. 1 reprints #1-11 and Annual 1998.
Avengers Assemble Vol. 2 reprints #12-22, #0, and Annual 1999.
Both books are primarily written by Kurt Busiek and primarily drawn by George Perez. The four-star review is directed toward the first volume, since I have not read the second. Based on other Avengers TPBs by this team, I would imagine it to be about the same quality: Quite good, but nothing exceptional.
The following should give you some idea of how this fits in to the Avengers timeline for any trade paperbacks you may already own for this time period:
Reprinted in Vol. 1:
Avengers: The Morgan Conquest (#1-4)
Avengers: Supreme Justice (#5-7) (also includes Iron Man #7, Captain America #8, and Quicksilver #10, which are not reprinted here)
Avengers: Clear and Present Danger (first half) (#8-11)
Occurs simultaneously with Vol. 1:
Avengers Legends Vol. 1: Avengers Forever (Avengers Forever #1-12) (starts between Avengers #9-10)
Reprinted in Vol. 2:
Avengers: Clear and Present Danger (second half) (#12-15)
Avengers: Ultron Unlimited (#19-22, 0)
After Vol. 2:
Avengers: Living Legends (#23-30)
Avengers/Thunderbolts Vol. #1: The Nefaria Protocols (#31-34 and Thunderbolts #42-44)
Avengers #35-40 (not reprinted(?))
Avengers: The Kang Dynasty (#41-55)
Avengers Vol. 1: World Trust (by Geoff Johns) (#57-62)
(Other "numbered" trade paperbacks continue from here)
Avengers Disassembled (by Brian Michael Bendis)
(Nearly all other Avengers TPBs take place long before any of these books.)
As noted above, Kurt Busiek's Avengers issues are quite good, but a bit unspectacular. The notes contained at the end of Assemble Vol. 1 detailing his original plans for the book are fascinating, and the George Perez rough pencil pages and Kurt Busiek script pages (for "Avengers #1 or whatever it'll be" as Busiek's notes call it) are intriguing as well. If you already own the three trades or the 12 issues reprinted here, it probably won't be worh bying again, but it would be worth browsing through at your local brick-and-mortar bookstore (or library, if you're lucky enough to have them carry it).
Again, I cannot comment in any detail on Vol. 2, not having read it, but having read all of Busiek's other Avengers trades, it seems safe to say that it would receive four out of five stars as well.
For readers new to Busiek, I would recommend the Astro City trades, Marvels, or JLA/Avengers over these books to see what all of the fuss is about. Most of Busiek's works (including Avengers Assemble, but not including Astro City) draw from the rich history of the Marvel universe, and are best appreciated by someone familiar with it, although other readers should still find these works fairly enjoyable.