I've included both mouthfeel and drinkability in one post since these commonly get confused and can sometimes wind up being included in one paragraph as if they're the same thing...they're not.
Simply put, mouthfeel is how does it feel in your mouth, not taste, but feel. Ignore the taste and sense the feel of the beer as it moves through your mouth. Pay attention as to how it crosses the lips, washes across your tongue, splashes up against the palate, brushes along the insides of your cheeks and hits the back of your throat. Is it silky, satiny, smooth, watery, thin, thick, viscous? These are primary concerns of mouthfeel.
The aftertaste is another element of the mouthfeel. How long does it linger? Is it pleasant, unwelcome, harsh? Another element is any alcohol "heat". Can you sense it readily? Does a high ABV beer mask the alcohol content well? If it's very present, does it overpower the taste?
Some reviewers will combine the mouthfeel into a paragraph with the taste since the taste of the wash is a natural segue into the feel of the wash.
This is the least understood attitude of beer tasting and many reviewers rely on a few devices to get through this one. Could I finish a whole bottle easily? Will the alcohol content impair my judgment? What foods does this pair well with? Is this a good example of the style? How does this one stack up to the other offerings from the brewery? I've used all of these, but just explain how easy it was to drink it.
The only time that drinkability is easy to address is when a beer is undrinkable due to a very negative element. The taste of a Belgian-style dark ale could be so phenolic that taking cough syrup would be preferable. The IBUs of an IPA could be so through the roof that you can't unpucker your mouth enough to take another sip. The ABV of a Russian Imperial Stout could be so high that you can't get another drop into your mouth...your lap, shoe or ear, but not your mouth. An American lager could taste so horrendous that you couldn't bring yourself to finish and committed that sin of all sins - you poured it. I'm not judging; drastic times call for drastic measures and I've been presented with beers that I just could not finish. It happens. Blame the brewery who produced it, not your dwindling manhood.
NEXT TIME: Holiday Brews: To Spice or Not to Spice
I hope this sheds some light on the two most misunderstood attitudes of beer tasting. If not, you're on your own; this is all I got.