I really like Hundred-Handed One.
My group was playing some Conspiracy: Take the Crown last week and things seemed to be going well for me. My deck was red-black and had done a good job bringing life totals down. Marchesa's Decree was doing Yeoman's work in keeping me from getting attacked too often, and I seemed to be able to get in for a few points of damage against someone each turn. I was digging for my remaining copy of Carnage Gladiator, hoping for a solid attack to wrap things up. Then one of my friends played Hundred-Handed One.
By the next round, the Hundred-Handed One was monstrous, handling defensive duties all on its own. Hundred-Handed One's not great against fliers, but the game had become a grinding war of attrition on the ground, and a 6/8 creature that could block every attacking creature was more than enough to handle anything the rest of the table could throw at it.
Hundred-Handed One is a great card  because it is useful from the moment you have four mana to cast it, right until the end of the game. As the game progresses it gets bigger and better able to handle the bigger creatures that hit the table. When a card can block any number of creatures, opponents start looking elsewhere. Everyone wants to make their attack count. No one wants to be the one who sacrifices their attack step and a few creatures just to take out a Hundred-Handed One.
Not surprisingly, the attacks against my friend disappeared with Hundred-Handed One on the battlefield. The real kick in the pants came later, when the Hundred-Handed One attacked for six.
And didn't tap.
It is easy to forget what an offensive threat Hundred-Handed One can be. Barring removal, you are probably going to have to chump block or give up at least two creatures to get it into the graveyard. It is the first line of the text box, but easy to miss when you look at everything else the card has to offer. Even when you see it, your thought is generally, "so it is still good on defense even if I attack with it." You are still focused on what a defensive all-star Hundred-Handed One is.
Vigilance isn't often seen as anything special in Magic. On Brushstrider, vigilance really doesn't offer much; the card is barely a speed bump on defense, so being able to block with it isn't a big deal. On Hundred-Handed One it gets a lot better since eight toughness and the ability to block 99 more creatures means you really want it available for blocking.
When determining which creatures should attack, whether or not you'll need the creature to block on your opponent's turn is part of that internal debate. You'll look at their creatures and determine if you're willing to take the damage, and how much damage you're willing to take. You'll look at which creatures you'll need to block to keep the numbers acceptable to you. Vigilance takes that part of the question and eliminates it. You can attack and it will still be there to block, assuming it survives combat.
And that's one of the differences between one-on-one games and multiplayer: when you are considering what you'll need to keep back to block, you have multiple opponents to consider. Players swing in with every creature in head-to-head games because the opponent has no creatures on the battlefield, or even a few creatures on the battlefield. They have looked at the situation and determined their opponent can't keep up if no one blocks. In multiplayer games, you may find an opponent with no way to block your attack, but there are two other opponents who would love a chance to catch you with your guard down, so you don't attack. This is one reason why multiplayer games tend to be longer than one-on-one games: even when there is an opening, you still can't attack.
Given this vigilance is helpful in one-on-one but a godsend in multiplayer games. With one opponent, there will be times when your vigilant creature will be irrelevant. You would attack even if the creature was able to defend. With multiple opponents, at least one of them will be able to swing at you, so vigilance on your creatures becomes relevant every single time you consider attacking. Vigilance allows you to exploit a weakness in one opponent without leaving you exposed to others.
If you wonder if Wizards of the Coast is aware of just how good vigilance is in multiplayer games, check out Conspiracy: Take the Throne: There's only four creatures with vigilance are in the set. Vigilance practically shuts down the goad mechanic!
Some people have referred to Aerial Responder as "Vampire Dayhawk" in an obvious comparison to Vampire Nighthawk.
Both are 2/3 creatures with flying and lifelink that cost 1CC. The Nighthawk has deathtouch while the Dayhawk has vigilance. My immediate thought was "Ooh, flying Dwarf! Bet that hasn't existed in Magic before!" Then I thought what would make a Dayhawk something that flies in the day. Finally, I thought about the comparison and decided it was unfair; deathtouch is far better than vigilance. Consider:
Deathtouch is better blocking and attacking, so this is easy. The only problem is that it can't do both but the vigilant creature can. The Vampire Nighthawk blocks better, but when it is time to attack, suddenly it is tapped and the deterrent that was keeping your opponents' creatures away from you is gone. Aerial Responder can attack when it is time, and plays defense when you need it.
How do you value a creature that isn't as strong as another on offense or defense, but does play both all the time? Vigilance offers that utility player who does it all. I won't say that creatures with vigilance are better than creatures with deathtouch in multiplayer games, but I don't think the answer is as cut and dried as you may have thought. That said, I'll likely take the Vampire Nighthawk over the Aerial Responder... in black decks and the Responder in white decks. They both look like good cards.
I'll be back next week, looking at the goodies Kaladesh has to offer. I'm holding out hope that I'll be able to crew a Pirate Ship or a flying aircraft carrier! What would the crew cost be for that?
P.S. I stole the game with a couple pieces of well-timed removal and main phase Sulfurous Blast. Grenzo, Havoc Raiser and Goblin Tunneller are a cute combo that keep the game moving. I'm loving this format!
 Is the Hundred-Handed One right or left-handed?
 This is often stated and often not true. A player with a slow start is often not attacked, since everyone believes they will get attacked if they try to take advantage. As long as your other opponents believe they will also be attacked if they capitalize on the opening you have left, they won't attack. This will let you attack with impunity. Note that this is not always the case, so take care with your attacks!
 Welcome to my stream of consciousness! Now you understand why it takes me so long to write art… oooh, shiny!