The Flaw in Flaws

I very much dislike the idea of the merits/flaw system. The idea is that you can select a flaw to gain a merit or a bonus feat (this variant is found in Unearthed Arcana). However, the premise as written is ridiculous.

If you are building a character that focuses on one thing, a flaw will almost never have an impact on your character. If you are building a character that only does melee, then taking a penalty to ranged attacks is meaningless. Penalties to skill checks are negligible to fighters, since they have so few skills to begin with.All the player is doing is accepting a worthless flaw for a free mechanical benefit.

Even if you are not min/maxing or specializing, flaws are pointless. From a roleplaying perspective, if I have always been terrible at ranged attacks, why would I bother to focus on ranged attacks later on in life? In everyday situations people employ the skills they are good at and don't worry about the ones they aren't so good at; people tend to hide their flaws or weaknesses. So mechanically and thematically, flaws are terrible. If you want flavor to your character, just play it out; there's no reason you have to take a flaw to play a flawed character.

But what if a player wants to take a flaw? First, ask them why. If they're doing it for a bonus feat, you may as well just give it to them and tell them not to worry about taking the flaw. If they're doing it for flavor, they don't need a (mechanical, rule based) flaw for the flavor, they can just do it.

An alternative to this system is to allow players access to bonus feats for flaws, but that you assign the flaw. From a thematic standpoint, the flaw shouldn't hinder what they're good at too much; if the flaw is too severe they wouldn't have specialized in that from the beginning. Make the flaw something that affects the player in situations.

If someone specializes in ranged attacks, perhaps they're almost neurotic about it. Give them a minor penalty to Will saves when they miss, reflecting a brief moment of doubt that overwhelms them. It shouldn't be crippling, but the players should feel it. This also requires that you work with the player to find something fair and equitable. The last thing you want to do is to make the character no fun to play.

Cinematics

The curse and blessing of playing RPGs is getting to watch action movies and shows and picture how awesome it would be if combat was like that in games.

It is amazing watching those things and picturing your current character doing them. Called shots, one hit kills, amazing feats of strength and acrobatics; all these things heroes can do in movies but recreating them in games is incredibly difficult.

If a player wants to do something epic (which is usually not covered in the rules), what can a DM do? Saying no is a terrible idea. Players become very discouraged when they can't at least make an attempt to do something and may rapidly lose interest the game. However, awesome is rarely in the rule book.

In a recent came one of my players was in the jaws of a T-Rex, about to be swallowed and another player was in the branches of a nearby tree. Tree-Dweller wanted to leap from the tree onto the T-Rex and run along it's back and attempt to hit it hard enough to dislodge the Snack.

The jump, climb, and balance checks are in the rules and "easy" enough to adjudicate. The smacking of a dinosaur hard enough to make it drop its food is not so easy. However, DMs are not supposed to stand in the way of awesome from the players. Setting a damage threshold seemed the way to go. While he failed to do the required damage; everyone was on the edge of their seats for the outcome.

Unfortunately, this type of awesome requires a few things.

1. You need to be familiar with the rules. Enough to think on the fly and be able to extrapolate from very specific rules to almost completely, unrelated situations. 
2. You need to be open to suggestions from your players. Many minds are better than one. However, don't let suggestions take too long or the tension of the moment will be lost. 
3. If consensus can't be reached, make a ruling. Too often games drag because of rules disputes. You're venturing into territory that will never be explicitly covered by the rules. When the final ruling is made, players can either agree or disagree. If they disagree, continue the debate after the game. 

The most important thing is to try and work with your players on this. There will come points where you may disagree, but efforts need to be made to meet them at least halfway. Part of the fun is being able to tell stories about how awesome encounters were. And sadly, awesome is never in the rulebook.