When it comes to the metal gear series, my favorite is MGS3. I found the start of Darkness for Big Boss to be well told and you feel the sorrow (hur hur hur) for all the shit he was put through. MGS4 is a big mixed bag for me. I loved it when it came out but over time, it has gotten worse and worse for me (hey, lets ditch the sneaking thorugh a battlefiled after only two missions) and the ending was a confusing mess.
MGSV on the other hand, ruined the serie for me. Excellent gameplay but an awful awful story and a waste of what could have been. Motherbase is overall, usless to walk around on, as there is not much you can do there. Punch your men can only bring so much joy, and the waste of the settings (Angola and Afghanistan) is also annoying. There should have been battles between the diffrent PMC in africa and fighting between the soviet and the Mujhadiens but nope. Didn't happend at all. You have this huge maps and nothing do in them apart from "consripting" soliders to your PMC. Most of the storymisions were boring as sin and the story in general was shit. A whole nothing in general.
Also, I think should have let you bring some of your pmc on the mission with you so they could do anything other sit on their asses doing nothing.