to be disappointing
[verb]
[te-gen-val-len, viel te-gen, is te-gen-ge-val-len]

“Tegenvallen” is used  when something does not answer to one’s positive expectations. The related noun is “tegenvaller”: disappointment/setback. When something is very disappointing, you can add a number of adverbs, see Extra.

You may often see a construction in the third person with an objective pronoun, for example: “Het valt me tegen dat…”, which translates to “It’s disappointing to me that…/It disappoints me that…”.

The opposite is the verb “meevallen” and the noun “meevaller”, which is used when something does not meet one’s negative expectations.

Examples:
– “Het miezert weer vandaag…dat valt tegen.” 
(“It drizzles again today…that’s disappointing.”)

– “De beurskoersen vallen weer behoorlijk tegen deze week.”
(“The stock exchange indexes are pretty disappointing again this week.”)

– “Het valt me vies tegen dat ik een bekeuring heb gekregen voor 3 km te hard rijden.”
(“It really disappoints me that I’ve had a speeding ticket for driving 3 km/h too fast.”)

Related words:
– Teleurstellen: to disappoint [verb] [stelde teleur, teleurgesteld].
– Teleurstelling: disappointment [noun] [de teleurstelling, de teleurstellingen].

Extra:
When something is very disappointing, you can add a number of adverbs. We’ve given the literal translation:
– erg tegenvallen: to be very disappointing.
– echt tegenvallen: to be really disappointing.
– zwaar tegenvallen: to be heavily disappointing.
– bijzonder tegenvallen: to be especially disappointing.
– vies tegenvallen: to be dirty disappointing.
– behoorlijk tegenvallen: to be quite disappointing.