I am a Romanian native, so I know quite a bit about it :D . Romanian has kept the major features, but it still dropped a lot. For example, instead of 6 noun cases, Romanian only has 3, of which only 2 are commonly used (the third, vocative - "hey, you, bird!" - is quite rarely needed; and even when it is, it's usually replaced with the nominative by most speakers - we commonly say "pisica rea!" instead of "pisico rea!" for "bad cat!"). There are also fewer verb tenses in Romanian than Classical Latin, and some are formed with auxiliary verbs instead of being truly separate verb forms. Also, the neuter gender, while technically existing in Romanian nouns, is simply masculine in the singular and feminine in the plural, there is no unique third form for adjectives or articles.

Slavic languages also have a case system (I think it's possible that this is part of why Romanian kept the Latin case system, as there was quite a bit of Slavic influence in Romanian), but they didn't "retain" it from Latin, as they are not Romance languages at all - they simply share this linguistic feature; Latin and Old Slavonic are by no means the only languages with a case system.