Far Cry 3 holds up really well, Far Cry 4 is mostly like 3, but with slightly better graphics and game engine, but a slightly weaker story. Far Cry 5 looks... different, but interesting.

I'd definitely recommend FC3, i haven't played much of FC4 yet, but 3 was definitely a good game imo.

Edit: forgot to mention - FC3 has one of the best villains in gaming history. The writing for his character was fantastic.