[I rate on a 4-star scale: 1-Too many problems to be worth your money or time, 2-Needs work, 4-Good and solid with a few nitpicks, 5-Love it/best in class. The third star in a five-star scale is too nebulous, IMHO.]
I picked up the Game Mastery Critical Fumble Deck during a sale at my FLGS on a whim. It's pretty solid, but I do have some complaints.
Most of the effects are good, but it's really missing some things:
* Effects for divine casters. What if your god doesn't like your prayer?
* Effects for psionics. What if you have a brain fart?
* Permanent physical disabilities: lost fingers and eyes; scars; burns
The magic user effects can somewhat be applied to divine casters and psionics, though not perfectly (especially in the case of psionics). I'd much rather have them be source specific, especially for the divine.
The "bleed"/ongoing damage effects seem to be a missed opportunity. It would make sense that you continue to take damage after losing a finger or taking a very deep cut, or etc., until you receive healing. Unfortunately those effects are pretty much not flavored at all. I can write this stuff in, but that really defeats the purpose of buying a product like this. There are a few physical effects that are nicely done--lost teeth and fingernails--and some temporary damage to seeing and hearing, but it's all pretty tame.
To pre-answer any criticism that such effects would be extreme and unduly harsh, I say the whole reason of using a fumble deck in the first place is to introduce an additional element of the extreme and harsh (amongst other elements, such as comedy) as a penalty for failure.
The cards look and feel pretty good, and are easy to read. The corners are a little sharp, maybe because they are so new, but whatever. The edges are pretty jagged, like the machine that cut them out of the printing sheets needed to be sharpened or replaced. It's really noticeable because of the black edges of the cards.
Unfortunately, the box the come in tore in half the first time I opened it. That put a very negative vibe in my head before I even had seen the cards! I'm going to have to use a rubber band now, which will significantly shorten the life of the cards.
All that said, I'll be keeping these for use with my 4E games. (They should convert extremely easily, for the most part. You'll want to be aware that "bleed" means ongoing damage. And you'll need to come up with a weapon and armor hit point system for a couple of effects, or rewrite them.) If any one of my complaints were fixed along with a better box it would be a 4-star product. If they were all addressed and the price came down it would easily be a 5-star product.