Whether it’s “all” bad or not depends on your expectation, but the question is kind of like asking whether all Bordeaux blends are bad. Cava is a little weird because it’s not a contiguous region, but a collection of areas, mostly in Penedés around the town of San Sadurní. But there are several subzones.
You might want to look at the wines you’ve tried and then find which categories you like or dislike most. The basic level of Cava is aged in the bottle for 9 months. But Cava follows the same categories as other Spanish wines. The Reserva is aged for 18 months now, and the Gran Reserva for 30 months, and then there’s the Cava de Paraje Calificado, which is aged for 36 months and which comes from specific sites.
Then there are seven levels of sweetness, ranging from Brut Nature, with no more than 0.3 g/l of sugar, all the way up to Semi-Seco and then Dulce, which can have over 50 g/l of sugar.
And finally you have the various grapes. The most widely planted is Macabeo, known as Viura in Rioja. It can be a grape that you either love or hate. When made as a still wine, it often has a bitter finish and it isn’t severely acidic. It’s a fairly old grape, dating back some 500 years or more.
Xarel·lo is quite different, with higher acidity and interestingly in spite of very light and thin skin, a good amount of resveratrol, more commonly associated with red grapes. It can make an excellent still wine.
The third “traditional” grape is Parellada, which makes the least interesting still wine and has no particular exciting features IMO. Most Cava is a blend of these three grapes. My suspicion is that the shower curtain notes probably come from one of these, likely Macabeo, which has the most “different” flavors.
But there are other grapes used as well. In Champagne, they would use Chardonnay, which can have a high sugar content and is therefore harvested early, even before it’s completely ripe. That gives the characteristic green apple notes to Champagne and can also bring those to Cava. Malvasia is often used for the sweeter Cavas.
Even more interesting are the red or rosado Cavas, made from Garnacha, Monastrell, Pinot Noir, and also a grape called Trepat. I happen to have a 100% Trepat from a small producer and it’s an interesting and very good wine, quite different from what you may think of as Cava.
So is “all” Cava bad? Well, if you have 9 grapes, seven sweetness levels, four aging categories, that gives you 252 possibilities right there. And then you add the winemaking decisions like what percentage of what grapes to use, the harvest dates, the specific sites, the winemaking itself, e.g. battonage, etc., and the possibilities become difficult to comprehend. The problem is that in the US, a lot of Cava is brought in by the two biggest producers and it’s sold cheaply. Then there are a few higher end Cavas available. But there are literally hundreds of small-production Cavas that are rarely found outside of Spain.
And while I’m not a huge fan of most sparkling wine, IMHO, no, it’s not all bad. Some is in fact quite good. 