I like rolling dice. I like making my players roll dice. Part of it is that I'm easily bored and rolling dice means that Something Is Going On both in the game and in the mundane world. Another part is that I like a character-centric game, which includes regular use of characters' mechanics to help resolve game situations.
And we brought all these dice with us anyway. Might as well use them!
So one of my favorite things about the 5e playtest is the advantage/disadvantage system. Getting to roll 2d20 and take the better one when you have an advantage, or having to roll 2d20 and take the worst one when you're at a disadvantage, is simple and neat and fun. It's like a house rule that made it to the big leagues -- a more entertaining option than the interminable bonus-stacking of some previous D&D editions, and more dramatic than the no-modifier-but-the-GM's-judgment of even earlier editions.
Have other games done this already? It's so simple than I can't believe nobody's done it yet, especially with the proliferation of systems that use a single die roll to get results. But I haven't run across it before.
Advantage/disadvantage also makes things more random... or are they less random? Mechanically, this will swing your chances in a predictable non-random way. But the execution of the mechanic will vary in a meta-random way. Some GMs will stick to offering it when the rules say so, i.e. The Boring Method. I'll offer it when characters and environments make it seem plausible and sometimes when table dynamics are such that we'll be more entertained, i.e. The Awesome Method. The key is that randomness helps the underdog. Most GMs like underdog PCs -- will we deploy this mechanic in a way that reinforces this? Will our PCs be able to use ad/dis to challenge ridiculous odds?
I hope so.
On the other hand, most PC parties are actually the overdog, capable of steamrolling the individual rooms and encounters and traps and everything else they stumble into. Event by event, they're the ones most likely to be hindered by randomness. Could be a fun dynamic.
It's a spiffy little mechanic. One thing does bug me. This is a Matt-specific complaint, I think, rather than a broad existential problem: I don't like mechanics that carry over. If something grants advantage/disadvantage, I want it to happen RIGHT NOW. Mechanics that you have to remember through X actions or keep track of for X rounds annoy the bejesus out of me. Having written a couple of (poorly-received) modules for Iron Heroes, I know that Mike Mearls is a huge fan of carryover mechanics, so I'm sure that this is just the way it is.
I can live with that. Maybe it'll grow on me.