What are some conservative features from Latin in any of the Romance languages?

Answer 1

One great example is that of Romanian, which, unlike most other Romance languages, still has cases (nominative, genitive, dative, accusative, vocative).

In Sardinian, Latin short /u/ remained, instead of becoming /o/. The Latin word siccus "dry" became sicu in Sardinian, but seco in Spanish and secco in Italian.

Italian has a conservative feature of its down: it kept Latin double consonants (secco as opposed to Spanish seco).