Since I just ran a game of Call of Cthulhu, including some rules and concepts from Trail of Cthulhu, I have spent some time pondering the qualities of the latter.
Why did I not just run a ToC game?
Basically, my main beef with ToC is that I don't really feel very comfortable about rolling one die. It might seem like a small thing, but I want more randomness in my games.
If you, like in ToC, rolls 1d6, may add in "spends" from your pools (all skills are pools of points) trying to beat difficulty of, say, 3-4, it goes without saying that most times randomness wont be a factor. Naturally, this is a design feature. Robin Laws who designed the game clearly states that his idea is to make the system drive a kind of narrative that behaves in a specified way.
Personally I like the quality of "new school" games, like the forge style games and others, to have rules that reinforce and drive toward a style of play the designer envision his or her game to be about. Many times, almost as many times that I have claimed Alignment leads to brain damage, I have elevated the rule of gold equals xp to sublime levels of design mastery, due to the effects it can have in enforcing a style of play. This is something I think is the great re-discovery stemming from Ron Edwards "system matters".
What kind of style is it then that ToC reinforce with its pools you can spend for basically guaranteed success? Well, it is a game where you can be sure, as a player, that the actions of your character will succeed. If you have a decent pool of at least 2, trying to beat 4 (a rough mean of a 2-8 scale) is an average chance of success of more than 80%. I think that makes it kind of pointless to have a randomizer with those odds. Before we delve too deep into math and probabilities, the main point of my argument is that on such a small scale a spend of one point, to say nothing of more than one, makes successes almost certain.
So, why is that bad? Isn't it good for the players to have say in when they get to shine? Well, no. Not when the object of the game is horror.
Horror demands giving up certainty and hope. Vagueness and isolation, and the strong possibility of failure and its following painful result is what drives the sense of horror. I think ToC is a fine game for CSI, but not for horror.
Some say the rules don't work that way in actual play, and they might be right. I have only played ToC once, but it did not falsify my principal objections to the rules. Feel free to disagree!