Romanian is the most widely-spoken of the Eastern Romance languages, with 25 million speakers in Romania, Moldova and adjoining areas of neighbouring countries (as well as in diaspora). Like the other Romance languages, Romanian descends from Latin, and retains some features from it that have been mostly lost in every other branch of the Romance family (like the neuter noun gender and noun cases); however, it has also been subject to significant influence from the Balkan sprachbund, impacting its grammar and also its vocabulary, which encompasses a great many borrowings from the Slavic languages.
Romanian has also simplified its grammar in many respects from that of Vulgar Latin. For example, while it retains a neuter gender, it is an “alternating” neuter that takes masculine declensions in singular and feminine ones in plural, rather than a gender that has its own unique declensions. It has also reduced the number of noun cases it has, from six down to three: Romanian has a combined nominative/accusative, a combined dative/genitive, and less robustly a vocative.
Its phonology has also, of course, changed from Vulgar Latin. One of the most noticeable changes to me is the loss of [kw]; in some words this simplified to [k] and in others it became [p] (like in apă from Latin aqua, or patru from Latin quattor). It also exhibits palatalisation in a number of words, presumably due to Slavic influence, so word-final i often means “the previous consonant is palatal” rather than [i].
Romanian’s vocabulary is only 20% words inherited directly from Latin, over 40% more recent borrowings from other Romance languages (mostly French and Italian), about 12% Slavic, 3.6% Turkish, 2.4% Greek, 2.2% Hungarian and 1.8% German. If you restrict yourself to looking only at the 2,500 most high-frequency words though, direct inheritances from Latin are the largest group, followed by later Romance borrowings and then Slavic. It was in the nineteenth century that Romania began to borrow all these Romance words, around the same time that they switched to writing their language in the Latin alphabet (previously it had been written in Cyrillic – and in Moldova it still was, until independence from the USSR).
In the area that Romanian is now spoken, there once (~2,000 years ago) was spoken another Indo-European language, Dacian. There are ~300 words that exist only in the Eastern Romance languages and Albanian that cannot be traced back to any Latinate source, which might be relics of this Dacian language.