Draconomicon II: Metallic Dragons is basically Draconomicon I: Chromatic Dragons, except that its about metallic dragons. This is the only difference. Hell, even the chapter layout and titles are identical: dragon lore, DM's guide, sample lairs, new monsters, and a hall of fame for kinda-sorta non-dick-move dragons. The art is mostly alright, but the page-count is about 20+ pages shorter...so the short review is basically that if you liked the first one and want more dragons then pick it up. However since I like to prattle on about shit I'm going to do just that, starting with the chapter I read first, New Monsters.
The real reason you're going to pick this book is is for moar stats, and Draconomnomcon: Metal Dragons has a crapton of them. Not only are there seven "new" dragon metals/alloys, but you get a wyrmling stat block for every fucking dragon printed thus far, draconians, something called a hollow dragon, coutls, drakes, kobolds, etc. Taking it from the top I'm going to tackle "true" dragons. The new flavors are brass, bronze, cobalt, mercury, mithril, orium, and steel.
Brass dragons are violent bi-polar mercenaries that are just as likely to maul the hell out of anything that wanders into their line-of-sight and loot it as they are to agree to contracted services. Talk about your Reverse Dungeon. Though they are artillery, they only have one ranged attack which has a short range and also automatically pegs every adjacent critter if it hits, which seems more like a controller to me. It otherwise can make multiple attacks and has a couple of close blast attacks that either push things or let it shift, which is good if you're supposed to emphasize ranged attacks.
Bronze dragons live by the ocean and demand tribute from merchant vessels, which has got to fuck with the local economy since I dont think they are too keen on actually spending any of it. On the plus side they really hate blue dragons and ruin their shit whenever they show up, which is kind of like buying a rock that is purported to keep tigers away. Not that I've ever seen tigers on a random encounter chart. Anyway...its attacks are fucking murder. The bite lets it roll out 20+ damage on average while the claws average 30 damage. The breath weapon deals a shit-ton of lightning damage, but if it hits anyone it can arc lightning onto another creature further away for 2d8 + 4 damage (with a push effect). Finally, it can dive underwater to heal itself and gain an attack bonus, which is really bad for a brute. I could see the DM having a pool of water for this fucker to use, and the players scrambling to keep it away.
Emo Cobalt dragons mope about in gloomy regions, like MySpace or the D&D Out of Print forum. The happier ones dwell in places with strong ties to the Shadowfell. They like to subjugate whatever local critter is handy and like high-school bullies pick fights to prove how "tough" they are. Sometimes if they kick your ass they'll let you go if you give them money, though if they can beat you up they might as well have a shakedown power that causes all your money to rain off of you. As controllers they are able to mix up their basic attacks quite a bit (bite-shift-claw twice), and the rest of their shit is a bunch of close blasts that pushes or restrains.
Mercury dragons function as draconic assassins (for...someone?), which is a bigger word for "lurker". As expected they deal more damage when they have combat advantage, and they can make a free attack against creatures that deals damage and applies combat advantage for a turn. Their breath weapon deals poison damage and renders the dragon invisible. Frightful presence stuns an assload of creatures so they have a couple ways to get that extra damage out one way or another. Finally, they have a per-encounter move that lets them turn into quicksilver, which prevents opportunity attacks, lets them squeeze through Tiny spaces, and if they return to their normal form? They get combat advantage against you.
Mithril dragons are crazy motherfuckers that can see into the future and teleport when they attack. Twice. Their prescience basically gives them a constant defense bonus, and they can also do an explodey 'port as an encounter power ala Prince of Persia: Sands of Time. Since they tend to devote themselves to causes and gods, they get radiant resistance and most of their shit has the Radiant keyword.
Orium dragons--and I'm not making this up--skulk about ancient ruins and literally command other creatures to, "rebuild the glories of yesteryear." Yesteryear. Why? Why not say ancient times, or something less...I dunno, silly. For that matter, why try and rebuild old ruins at all? I guess I wouldnt complain since of all the metallic dragons they seem like the nicest out of the bunch since they dont randomly maul and/or extort things that are not dragons. All sillyness aside, their breath weapon is pretty cool, generating minion brutes each time they use it. Otherwise they're pretty basic with a predictable bite/claw routine while they wait for dragon breath to recharge.
Steel dragons seem to enjoy touring around in humanoid form and try to undermine authority for some reason...perhaps because they're the only dragon that can use change shape by default? I dunno. I guess if I could do that and was really bored I might do random shit like that. Otherwise they have a wing attack and can implact a suggestion as a minor action that slides, causes the target to grant combat advantage, and lets the dragon shift a square. Elder steel dragons are more interesting in that they can shape their breath weapon into a force cage and trap creatures.
There are also wyrmling versions of each metallic dragon, including the ones that were in MM2, so hopefully you werent like me and sold all your Small-and-Medium sized dragon minis when you heard that the (at the time) youngest dragons in 4E were gonna be Large.
Hollow dragons are the leftover dragon skin empowered by the dragon's inherent elemental energy, soul-type essence. So...kind of like a maybe-less-morbid version of the dracolich. They arent all good (as metallic dragons likewise are not), they rupture essence when hit, and larger versions can swallow you and trap you inside their animate flesh and cook you. Nifty.
There are a pair of couatl blocks, one evil and the other unaligned. They have ongoing poison bites, deal more radiant damage when hit by radiant attacks, and can make extra saves against immobilize and restrain conditions.
Eight draconian types get represented, meaning that a few corrupted metallics get left out (mithril, orium, steel, and mercury I think). They still have their various death effects, and there is a fair spread on levels and roles so I could see it being very easy to do lots of mid-to-high heroic tier using draconians as primary threats. At least I have a use for those old draconian minis that I couldnt pawn, and I didnt have to buy a craptastic Dragonlance book for the stats!
Drakkensteeds are mount-types that have an impressive overland flight speed of 15 and a dazing roar. When you burn an action point they auto-recharge it and use it for free. Nifty, but 16th-level. The epic-undead version also grants necrotic and poison resistance. Too bad they look fucking stupid, as I am a shallow player and aesthetics play a big part in the decisions I make.
As before there is a section on swapping out alternative powers, and a template that actually downgrades dragons to Elites for better use in level-appropriate group fights.
After that I decided to take it from the top and browse the chapters to see if anything caught my attention. The first chapter--Dragon Lore--goes over how dragons were created before moving on to a brief recap on their physiology, with a few paragraphs devoted to shapechanging. A sidebar refers you back to Draconomicon I for better coverage since they didnt wanna reprint a bunch of content again.
What I find most interesting about this chapter is that it puts a spin on how metallic dragons used to be represented: instead of being Good they're now
Jackass Unaligned. Many believe that they are superior to mortal races aside from just level and Solo category, and while some might wish to help us they tend do look at mortal races as primitive creatures that need their assistance and expect gratitude in exchange for the privilege of receiving it. This perspective makes it easier to utilize them as villians without sacrificing consistency and credibility...in case you needed the books to encourage or even "allow" you to do so.
The rest of the book follows the format I've come to expect for the other "monster" books. You get a chapter with stuff on sample lairs, organizations, traps, some new artifacts, and ways to use dragons for the long-term in your campaigns.
I enjoyed Draconic Encounters, as it provides ways to properly manage dragons with your XP budget and I've had plenty of DMs use dragons with minions in a way that has hosed many a character. So, hopefully budding DMs can be bothered to read this short section on how to do a job proper (or at least less lethally).
Otherwise...not much else comes to mind. Thats it. Book o' dragons. Get it if you want/need more, or want to see some various methods to build solo monsters. You might get some mileage out of the lairs and traps.