Umbrian phonetics lost some of Indo-European vowels, practically all diphthongs, and it had a strong tendency for disappearance of final consonants. Final -d was lost, s between vowels and in final position became r under the rotacism law (it was much stronger than in Latin). Two strange sounds were invented, which are still being discussed by linguistics: a sibilant which was used instead of k between vowels, and a sound which is transcribed as  and was transliterated by Romans as rs - maybe like in Chech diacritical r. This sound was sometimed used in intervocal position (between vowels) instead of original d.
The Umbrian alphabet is likewise of Etruscan origin. The letters T and K served for the /t/ and /k/ sounds as well as the /d/ and /g/ ones. A modified R, much like a capital P, denoted a sound which was transliterated in Latin as RS. One new symbol was used for a sibilant Ç.
Umbrian morphology was much alike Oscan, and changes did not influence
it. But some linguists note that Umbrian was the most progressive of Italic
tongues, and there was a trend of losing some flexions and complex verb
forms. Umbrian was the first to influence Latin, as it did not disappear
in first centuries AD, and many guess, that this language was one of the
main mothertongues of Popular Latin. But Latin after all assimilated Umbrians,
and we can judge about the language using just ancient texts, of which
the Iguvian Tables are the main source. Umbrian grammar is very interesting
and will be soon published here in our Indo-European