As a BJCP judge, and additionally from my liver’s experience of dranking so many effing beers, and in addition to my beer-literature readings, I would have to say that eXXXtrack beers’ main negative issue is “oxidation.”
That is to say, a ‘cardboard, stale’ flavor and aroma. I am able to pick out eXXXtrack beers by smell, before I even am within 100 yards of the room hohohohohoho! that was a fib. But seriously they Are pretty apparent. I wish I could go back in time and taste a few of my eXXXtracks. I thought they were so damnable gooowd back then.
The thing is, as at leas one previous writer commented - you gots ta git da FRESHest eXXXtrack available. I believe the common, negative denominator in eXXXtrack brewing is OXXXidation (cardboard, wet paper, stale, whatever). Or perhaps a metallic, tinney flavor.
Goto All-grain ASAP and you’ll never regret it.