You're not missing much by skipping OG Persona 4. OG has 2 different voice actors than Golden which some people prefer. Golden is also easier, but it also added a higher difficulty that makes up for that somewhat. Marie's story isn't the best, but I feel like it helps to make the true ending seem less out-of-nowhere.
Besides all the other stuff mentioned, P4G's shuffle time system is a lot more enjoyable than the old system (which was reflex-based).
I know people are nostalgic for the original, but I can't go back. Lack of portability, longer load times, no widescreen, no fast-forward option, worse shuffle time system, having to retry fusing over and over to get what you want, fewer ally abilities, plus a lot less content.