On my private list of "Horrible things that Cthulhu did to mankind" there's Black Plague in the number one spot, but then there's this card in close second place.
Encounter cards are like Twinkies: sure it might be thrilling to have one once in a while, but eat too many at once and boy, you know you're in trouble. Having to draw one encounter card per round is the norm. If you are a mystic at heart you have cards like Drawn to the Flame that gives you 2 clues for your trouble, or Delve Too Deep to gain that precious XP. Basic Weaknesses obviously lie in different category than regular player cards, but I want to sketch out the idea of how much enounter cards are worth in terms of gain, so that, by analogy, we can try to understand how much you lose if you draw a bunch of them - which will happen at some point, if you find yourself mildly Overzealous.
All Basic Weaknesses (excluding obvious Indebted) deny you draw of one card and additionally put on you some kind of penalty: some of these penalties are immediate (like Amnesia) other give you time to deal with them, before they start to become the problem (for example Psychosis or Chronophobia). (Additionally, that shows the standard of how much inconvinience average Basic Weakess should provide: aproximately loss of two actions - assuming you don't want to suffer consequences.) Obviously the immediate ones tend to be worse, mainly because you have no control over them, they don't offer you any substantial choices. Overzealous, sadly, belongs to the first group, but the worst part is yet to come.
Now, let's see what happens, when you draw Overzealous during your upkeep:
- denied card draw;
- you draw at least two encounter cards, PLUS one more in mythos phase: effectively, you draw at least 3 encounter cards before you can do anything again;
- your prognosis of the start of your next action phase might be extremely different.
One might say: "Bah, of course it's gonna be different! Tis the Arkham, you fool!" - and on that note I agree, but it's all about the scope. You expect to get hit by something, or to be engaged with one enemy at the start of your next turn... But what about having three enemies on you, or having just one, but being severely damaged due to failed skill checks? Or pulling a bunch of Acolytes and learing that whoops! - agenda is going to advance two rounds earlier...? That's a different beast entirely. Additionally, this card, unlike other Basic Weaknesses, scales with the scenario you're playing, meaning that the harder the scenario is (or the later in the campaign you are), the worse Overzealous gets. Drawing this one card, like no other Basic Weakness, might be the end of the road for you, just by the fact of how little control you have over it and how far it can set you back, compared to other Basic Weaknesses.
Are there any good news? There are! In multiplayer it's much easier to deal with the encounter cards with staying effects (mainly enemies), as your friends can always help and taunt them off you. Another good news is that if the first encounter card drawn from the revelation effect already has surge, that card cannot gain additional surge! Hooray...? Bad news is that if the second card drawn from the surge of first card, has surge, you will chain even more encounter cards. So there's that.
This encounter card is probably the worst weakness for true solo decks, as it will thoroughly test your luck stat - which sadly, you can't boost. However, even in group play there will be times, when you'll draw perfect storm from the encouter deck, and in your powerlessness, you will weep: "Cthulhu, deliver us!" But in return, thou shall only hear chaos tokens, shuffling in the bag of tentacle wonder. And you will repent for not believing this review.