I wouldn't bother with 4; it's virtually the same thing under a different coat of paint. Blood Dragon, on the other hand, literally is the same game with a different coat of paint and so, for me, the novelty of it all wore off pretty quickly. Basically, if playing through 3 was a chore by the end, I wouldn't recommend jumping into either.
Funnily enough I really quite enjoyed 4 and thought 3 was basically bollocks. I thought they did a few things different enough like the awesome mini helicoter and the setting was different for it to be more fun.3 had Vaas but I was bored of the setting and the main characters and story was utter utter shite.
But yeah all very similar in style really, I was hoping Far Cry Primal would be more immersive/like FC2 but it basically looks like Far Cry 3 with sticks.
Nice!
Now watch it be windows store only lol.