In an event not seen in almost a year, Valve has released two hero-bearing patches in a row: Bristleback last patch, and Skywrath Mage this patch.
Skywrath Mage is long range artillery in the purest sense of the word. All of his spells have longer than average cast range range, beating out the basic attacks of any hero except Sniper with Take Aim maxed out. Arcane Bolt (his Q; scales off of Int) and Concussive Shot (his W; AoE damage/slow) are also unique in that they always hit their intended target, regardless of going invisible, blinking, creating illusions, or using any other form of disjoint except Eul's, Astral Imprisonment, or Disruption. Arcane Bolt and Concussive shot also provides flying vision of the projectile's path, which means you can always tell where the target has run off to, although the target must be visible to Skywrath at the time of spellcasting for the homing properties to kick in. He cannot Concussive Shot an invisible Riki sitting on top of him. The cooldown on Arcane Bolt is also impressively short – 5/4/3/2, with a piddling 70 mana cost - which means he can spam it without worry.
His E, Ancient Seal, can be thought of as a poor man's Orchid. It silences the target for 3-6 seconds - depending on level - and amplifies all magical damage the target takes for the same amount of time. His ultimate, Mystic Flare, is akin to Sunstrike: it deals lots of magical damage to every hero in an area over two second, ignoring creeps, illusions, and any other chaff in the way. So he could, say, cast Concussive Shot on a pack of illusions, spot the real hero, then use their slowed state to drop Mystic Flare on them.
He has an "impressive" 511 base HP, (+27hp/lvl) and 0 base armor, which puts him in such prestigious company as Doombringer and a newborn kitten. While his basic autoattack does respectable damage, the animation is rather slow and his +.8 agi/lvl means his attacks will always come out sluggish. He should constantly spam Arcane Bolt instead of autoattacking to make use of his high base intelligence and excellent intelligence growth. This guarantees that he'll always be something of a threat as long as he keeps up in levels.
You will typically see Skywrath as either a safelane support - using his nukes to keep down lane opposition - or as a mid-lane if the player is feeling cocky. Just about any powerful mid hero should be able to punish such a player, thanks to Skywrath's hilariously bad HP pool and complete lack of armor at low levels. He cannot carry as he has no means to farm up items quickly, his nukes are all either single target or do not effect creeps, but he will always do respectable damage to the enemy as long as he keeps up in levels. He also has no way of dealing with enemies who can close the distance on him - such as Riki or Queen of Pain - besides casting Concussive Shot and running away, making him an easy gank if you can take him by surprise.
If you plan on playing Skywrath, your first priority should be dealing with his abysmal health and armor with something cheap like Drums. You should then buy a force staff and/or a Eul's specter so you can escape ganks or help set them up. Another good item for him is the Rod of Atos; the combined slow from its active and Concussive Shot will wreck anybody's day and force them to endure the full might of Mystic Flare. It also gives Skywrath a nice boost to his health and mana pool.
Overall, Skywrath Mage isn't a bad hero. His scaling nuke means he hits harder as the game goes on, and his slow and silence bring a nice amount of utility. The fact his spells are all long range and can't be disjointed means he is an excellent hero for standing outside the fray and and casually flinging nukes. He's also excellent at popping Linken's Sphere with Arcane Bolt to help catch elusive heroes that typically buy it. Don't expect to see him picked competitive play, though; the push-heavy nature of games these days means his utility is somewhat limited. He can't quickly clear creepwaves and he doesn't bring the early game pain the way many other support heroes do.