Book two of the "MOAR lootz" series, Adventurer's Vault 2 is a more comprehensive-yet-thinner version of AV1. Still, even at $30 its a good buy, as it rounds out the selection of magic items that were missing from many PH2 classes...namely anything that relied on a totem, swordmage, and bard. There arent any new mount or companion slot items, but it makes up for that with some new item types: ammunition, lair items, tattoos, immurements (a sub-category of consumables), and item sets. For the story-nuts, many magic items have a sidebar that goes into a bit of history about that particular item. By now you should know what the old slots do, so I'm really only going to talk about the new things since this book adds more than a few new things to the mix, and really you dont want to buy a book if the new stuff is crap.
First up, ammo. Ammunition items require that you use its enhancement bonus, even if worse, if you want to benefit from its property. You can opt to fire it without activating it, in which case have fun launching 50+ gp arrows for no particular reason. Even though you cannot stack the enhancement bonuses, its still handy since you get both the weapon and ammunition crit benefits and can still trigger weapon powers if you want. The downside? Its like, 30 fucking gp a pop for the cheapest of arrows.
Which is really the reason why they make you use the ammunition bonuses: so players cant just buy the cheapest stuff and still garner nifty bonuses like, "if you hit an enemy with an attack, end one conjuration or zone that enemy has created." Daaayam. I never bothered with magical arrows in 3rd Edition, but I might now. Josh plays a ranger, so I'll just start dropping stuff like this and see how he handles it.
Lair items were the cause of much consternation on the forums. I know, its the forums, and everything causes consternation there given enough people and time. Wondrous lair items are wondrous items that are not portable. You have to leave them in your "lair" for them to function, which means that in most traditional D&D games they arent going to see a lot of mileage. I can see how these would be handy in an urban campaign, or a more specialized one where the DM gives the players a homebase (hell, Age of Worms had one). I can also see why people decry them as useless or worthless, but frankly its a whopping two-and-a-half fucking pages. Most of the books from Revised Edition had TEN TIMES as much wasted space, so I'm willing to make a concession here.
Lets see...tattoos are next. You get one by having the ink done through various means (it makes mention of eladrin altering the skin with magic), and then using Enchant Item to make it do whatever the hell you want it to do. You can find tattoos and then apply them to your skin in a similar fashion as those lame-ass temporary ones that you might have gotten as a child due to a lapse in judgement, but hey, it worked in Planescape: Torment so who am I to judge. Unlike past editions, they're un-slotted wondrous items with no apparent count limitation, so go nuts if you got the cash.
Immurements were formerly orb implements that let you create pocket dimensions to fight monsters. Now, they are extremely expensive fire-and-forget terrain deformers that alter the battlefield for a short period of time (end of the encounter), though one of them has a daily power that lets you fly a short distance before falling back to the ground. The concept seems cool, but I'm going to have to drop one as a treasure parcel in order to get my players to use one. Hmm, what about an "immurement of Cyre's echo"? Yeeeeeee...........
And that leaves us with item sets. The item sets are one of those things that I'm sure people are going to see and ignorantly tout it as proof that D&D is, "just a vidjya game", considering that A) Diablo 2 did it first, and B) so did 3rd Edition. Anywho, item sets are a collection of thematic items (dur) that function like normal items, but if you or the party have 2+ items from the set they each get an additional benefit. Now, I say you or the party because there are sets that function if one person gets them all, and then there are "party sets" that work if multiple people carry different items from the set. Still with me? Good. Usually the granted benefit is something fairly minor like a skill bonus (which can be a flat bonus or equal to the number of items you are packing) or improves a class feature thematic to the set, but sometimes its an actual full-blown power.
Example: Zy Tormtor's Trinkets
Since I like warlocks a lot, I'll just use this as an example. Its got four items to the set, a wondrous item, hand item, weapon, and neck item. The blackleaf gloves let you teleport once per encounter when you trigger your pact boon. The pact blade does what its always done, and the specific weapon depends on whatever the DM wants, though its cited as, "usually a dagger or sickle". The prison of Salzacas is a wondrous item that lets you conjure up a spirit that can move around, pick up shit, and drop it. Kind of like a more reliable R.O.B. Finally, the spidersilk mantle gives you a climb speed once per encounter.
So, by themselves they're decent enough. If you get 2-3, you get a bonus on Thievery checks and always act like you have thieves' tools. If you get all four, then you can use as a daily power, which lets you originate any warlock power from the prison of Salcazas instead of you.
In The End
If you have the patience and DDI, you can pretty much just ignore this book and wait for Character Builder to update. It (probably) wont have the story content for many of the magic items, but otherwise you'll be getting the entirety of the book that most people will rely on in an easy to navigate and reference format. On the other hand, if you despise DDI (because you are a fool, fool I say!) then yeah, you're going to want this, especially if you play classes out of PH2. Even if you dont use PH2 at all, there is plenty of new stuff to make it worth your while.