Portable Ops also takes place before MGSV, but it's somewhat murky canon and thus far not relevant to the plot, so you're fine ignoring it for story purposes.
Portable Ops is partially canonical. The San Hieronymo Incident and a few points are important, later Peace Walker moves on from much of what happened after that point.
As far as Solid Snake goes. MGS4 is one of those things you can either take or leave. It brings a bitter and redundant closure to every single event and character that was not really needed. In the long run who's characters benefit the most by the end of MGS4 are Raiden, Big Boss and Zero with Mei-Ling, Drebin and Little Gray being the most enjoyable out of all of them.
Also, the main problem with MGS4 is that is the continuation of the metanarrative with a life lesson
that MGS2 is. Most of MGS2 wasn't intended to be taken literally, nor it was a sequel in the tradicional sense to MGS1. Not to mention that is very clear that MGS4 acts as a slap in the face for the most stubborn hardcore fans out there on purpose. Honestly, I recommend taking MGS2 as the true ending of Metal Gear like it was intended to be, check out Metal Gear 2: Solid Snake and leave MGS4 as The End of Evangelion of the series.
@Yggdrasil maybe aside from peacewalker as that had a lot of content, every mgs title (1, 2, 3, and 4) combined are still shorter in terms of playable content than MGSV. Hell even straight story, V seems to be leaps and bounds longer. And before you try to say something like "well if you aim for everything in the older games..." then yeah that would carry over to mgsv as well and you'd still have that much more content in V then the first 4 combined. I give peacewalker props though as it does have a boatload of stuff to go through, though not as long as MGSV by a longshot.
Oh, you were talking about 'content and experiences'. I don't see gaming in general from that angle since there's so much to it than just some marketing terms. But yeah, every MGS has always been bigger than it appears to be. Some more than others but there's always a huge amount of depth if you dig.
Either way, I genuinely didn't know what you meant before so thanks for replying back.