In order to get in some geeky time despite our 'no-screens' policy when it comes to our son, I've been soloing some adventure card games (ACGs). These are cooperative, table-top games based around building decks of cards that represent the player's skills, equipment, and talents used to overcome the challenges spewed forth by decks representing enemies, situations, and weaknesses. A big appeal to these games is that, unlike static board games, expanding or changing the game is a simple as adding or removing cards, thereby keeping the games fresh. The current darling of the ACG world is Fantasy Flight Games' HP Lovecraft inspired Arkham Horror: The Card Game (AH:TCG), which introduces some neat new features that I wanted to discuss.
A neat aspect to how these ACGs are handled is that they're organized into 'campaigns', in which players face increasingly difficult scenarios whose completion rewards them with increasingly powerful cards for their decks. The problem is that some ACGs don't have a heck of a lot of variety to the scenarios: pitting your cards with ever increasing modifiers against the enemies' increasing modifiers tends to get a bit old (I'm looking at you, Pathfinder).
AH:TCG goes a long way towards solving this by adding two piles of cards to each scenario: one representing the player's objectives (the 'act' deck) and one representing the machinations of the opposing, evil forces (the 'agenda' deck). The act deck advances by solving objectives that vary from scenario to scenario while the agenda deck advances over time, creating a race against the clock. Reaching checkpoints on either deck has consequences that can change the playing field, add or remove challenges, or alter objectives. These decks are very cool and are applied in unique ways in each of the five scenarios that have been released so far.
The act and agenda decks also introduce a 'game book' aspect to the campaign in that they're set up in such a way that each scenario offers multiple paths to completion. While some are simply 'fail' states, others offer decisions that will influence the resources and difficulty of future scenarios in the campaign. Furthermore, there's a campaign guide that has you read particular passages based on the choices that you make, tying everything nicely into a single overarching narrative. Because of the multiple paths resulting from your choices, there's also a nice degree of replayability as well. At the moment, deck-building - accomplished by spending experience earned during scenarios - is somewhat limited by the cards that come with the default set; but this should improve with future expansions.
Overall, the basic gameplay of AH:TCG is quite a bit deeper than previous ACGs that I've played, offering a wealth of interesting options and tough choices during each scenario. There's a lot of spinning plates involved in each adventure, and each choice involves clear opportunity costs that lead to nail biting outcomes, as any good game should. During my first couple of rounds of the game I was enamored with its systems. But after I completed the tutorial missions, I found that the game's difficulty spiked through the stratosphere, and in a very frustrating way.
I've played several of Fantasy Flight's products, and one thing I've noticed is their penchant for placing a lot of weight on chance, as opposed to European boardgames, which tend to minimize dice rolling. In order to use skills in AH:TCG, players compare their skill value, say three, to a target difficulty, say four, and if they meet or exceed the value, the test is successful. As is typical of these games, cards offer many ways to modify and improve your skills. Once all of the modifiers are chosen, the player must draw a 'chaos token' from a bag, and apply its effect to the test. The overwhelming majority of these tokens are negative, applying a penalty to the test, such as -2 or even -5. However, some number of them - five out of 16 tokens - have a scenario-specific effect that can be utterly devastating.
See, you can plan around negative modifiers during important skill tests by playing cards such that you exceed the required target value. But when a bad draw from the chaos bag causes you to auto-fail an important test, or worse, advances the agenda deck and causes you to lose the scenario, it leads to table-flipping frustration. This is a huge problem: without the randomness, the game is already strongly stacked against victory. But when you throw in a unreasonably high chance that any skill test will lead to horrible consequences, it's a recipe for disaster. In seven games, I've lost two outright due to bad combinations of 'rolls' and draws leading to instant character death or enemy victory. In several others, chaos tokens alone have resulted in sub-par scenario endings, making subsequent scenarios effectively unwinnable.
Most comments that I've read have criticized the chaos system because, even though you can adjust the difficulty of the negative modifiers according to the printed rules, the devastating 'special' tokens frequently undermine even the most carefully planned or inventive strategy. The occasional defenders of 'chaos' argue that this frustration is consistent with the Lovecraftian themes. For my part, I'd argue that the only thing that matters when it comes to producing a game is that the game is fun, or at least interesting to play, and AH:TCG's chaos system pulls the rug out from under what is otherwise a very ambitious effort.
I'm hoping that that future expansions rebalance the game away from screaming frustration as has apparently been the case in previous Fantasy Flight products. The difficulty is really the only thing I don't enjoy, so I've begun playing using 'house rules'. Essentially I'm removing those tokens from the bag that have inescapable consequences (i.e., auto-fail or advancing the agenda deck) and replacing them with tokens that apply negatives that can be mitigated via good strategy. You can call me a wimp and and a cheater all you want. If it makes the game more fun to play alone in the dark after the family has gone to bed, I don't care.
 That is, playing them by myself. It's sad, I know. But as a dad, you take what you can get.
 While at first I asked myself why the game doesn't just use dice, I realized that the chaos token bag is an elegant solution to being able to tune the game's difficulty. There are many more tokens than you use at once, so if you want the game to be more difficult, you add more negative tokens or vice-versa. My problem is that the difficulty rules only focus on changing the modifier tokens: the devastating special tokens are included for all difficulties (though their effects are increased even further at the higher difficulties).
 See this forum thread, for example, where people ask whether anyone has actually, legitimately managed to successfully complete the last scenario of the campaign.
 I should point out that some of the playable character's abilities allows you to redraw tokens from the bag or otherwise flip their modifiers. While this is a way to deal with the raw chaos, I'd argue that it's a poor solution because it forces you to play with those characters or suffer the full brunt of the chaos system.