Black Cat espresso is the flagship product of the now officially world-class cafe, Intelligentsia. Because of its fame, widespread availability, and quality, I think that calling it the bar by which other espresso blends are measured is not an exaggeration. I'm a big fan of Black Cat and buy it quite frequently and this product review has been something of a late comer.
First thing that someone coming from Starbucks or grocery store coffees will notice is how light the roast of Black Cat is. I'm not entirely sure what it was, but for whatever reason, America has grown accustomed to super-dark coffee roasts. This has benefits and detriments, of course. Dark roasted beans can make anything taste acceptable, so that's good, but it does that by erasing the terroir of the beans, which for good beans is bad.
The best espresso roasts are loaded with sweetness, chocolate, caramel, with the roasting process creating not char, but the flavor of lightly toasted bread. You don't ruin this with a dark roast! Go try local roasters and their espresso roasts. You'll find that many of them, if not most, will have espresso roasts in the city to full-city range, with some even including roasts as light as half-city. Again, the exaggerated flavor of the espresso process brings out everything the beans have to give, so more so than any other process, espresso demands good beans.
Black Cat is a case study in this. It's rich and smooth, and even when you screw up shots it tastes pretty good. When you get it right, it tastes amazing. I must admit to preferring my espresso a bit richer than Intelligentsia shot for. They obviously want a bit more complexity, which they openly admit, whereas I am totally happy to have espresso marked almost exclusively by chocolate and caramel. This is not a knock against it, obviously, since they are skilled roasters shooting for a specific flavor profile and they achieve that goal with aplomb.
That being said, there is one thing that pisses me off about this roast and that is how easy it is to screw up. It's a very light roast and this means that your espresso machine is going to be hyper-finicky with it, frequently side-channeling and wanting you to change your grind level from day to day. It can be a major pain. It's aggravated if you have an already pissy machine, like my La Spaziale Vivaldi II.
But that's my problem, and yours if you choose to use BC, and the only thing that is a true knock against the beans are the price. They are rather expensive at well over $1 per ounce. You can buy them cheaper from other retailers (Like NeedCaffeine.com) than through Intelligentsia... for some reason... but it's still far more expensive than other famous blends, like Stumptown's Hair Bender or local blends like that which can be had (in Rhode Island) from Updike's Newtowne or New Harvest.
To put a point on this whole discussion, Black Cat is a high-quality espresso. It's worthy of its fame, and, while expensive, tastes fantastic. You would be well-served to drink this if you like espresso.
Black Cat Espresso: Highly Recommended