Versimilitude is a word that I find neither easy to spell, nor easy to say. Nor do I find it easy to read in other people's posts. So much so, I think it should be banned from the vocabulary of gamers everywhere.
Why? Because it has become misunderstood and fetishized among rank-and-file gamers to the point where it has lost its value in gamer discourse.
I say this because, while it is a perfectly useful term for game-designers to use and apply, its adoption and abuse by those people, like myself, who intend to play games, not design them, has reached noxious levels.
The standard definition of versimilitude is that which exhibits the appearance of truth or reality. Versimilitude, if properly understood, should be considered more the former (truth) than the latter (reality). That is, something can exhibit the appearance of truth, but may not reflect reality, and still have versimilitude.
The problem is that many gamers tend to focus on the "reality" portion of versimilitude, not understanding that games, by their very nature, are fractured images of reality. The point of games is to abstract reality. If I want to experience reality, I don't need a game for that, I simply walk out the front door. But games that are well constructed can both exhibit abstractness and versimilitude. A game does not have to mirror reality in order to exhibit versimilitude.
For example, Live Action Role Playing games ("LARPS") are among the most realistic role-playing games. What could be more realistic that actually "being" the character, rather than abstracting it to a set of attributes? I don't roll dice to see if I hit, I take a swing at you. I don't tell the DM what I say, I say it to the other LARPer.
That does not mean that a LARP has more versimilitude than, say, Tigris & Euphrates, which is a very abstract game.
A game can exhibit versimilitude, and be completely abstract. That abstract game can be said to have versimilitude if its game mechanics are internally coherent, and is tells "truth" about a particular facet of reality.
I also see versimilitude being fetishized by some gamers, using the term as a sort of "litmus test" for whether a game is worth playing. Risk is a game that, in my estimation, has a very low level of versimilitude. What truth is Risk trying to model? However, this would not prevent me from playing, and enjoying, that game.
Similarly, I see a few in the pro and anti 4e communities still arguing for and against 4e on the basis that it demonstrates, or fails to demonstrate, versimilitude. I'm not interested in injecting myself into that debate. Frankly, i'm not terribly interested if it does or doesn't. Role-playing games are very complicated models of reality, and I do not believe there will ever be an RPG rule-set that meets every gamers version of reality.
Are you enjoying the game you're playing? Then just play it. If there is a rule that fails to exhibit versimilitude, then change it. It's your table!