On its own, Revengeance is pretty self-contained. It's far enough separated from the events of MGS4 that there's not a lot of legacy stuff you need to be aware of to understand the main thrust of the story. That said, there's a ton of stuff on the periphery of the experience that is going to go way over your head, and a handful of things that are completely glossed over because either you know or you don't and the game isn't going to bother to try and explain it.
I'd say that Revengeance is fine as your last Metal Gear or only Metal Gear but horrible as your first Metal Gear. If you have any designs on ever touching the rest of the franchise, then save Revengeance for much, much later.
Previous plot points are occasionally brought up, but having knowledge of previous Metal Gear games isn't really necessary for enjoying the game at all or even just following the plot. If you wanted to get into the series I'd probably recommend starting with MGS1 (or the original Metal Gear if you want to go as pure as possible), but Rising is a much better starting point than 2 or 4 IMO.
4 especially will just be incomprehensible if you didn't play the earlier games, and I personally think it's a bad game. The one thing it has over the rest of the Solids are the controls though, which would make going back to earlier entries hard.
A lot of things are going to be pretty confusing or just seem bizarre if you run through Revengeance as your first Metal Gear. I'd at least check a wiki or something for Raiden's backstory, or play MGS 2 or 4 to get an idea of how weird and crazy technology is in the Metal Gear universe.
Revengeance's plot is pretty straightforward and cut off from the plots of past games, but all of the elements that make it up are brought from things explained in previous Metal Gear games in kind of a brilliant way. If you know about the Metal Gear universe beforehand, then what's going on will seem kinda awesome. If not it'll just be bizarre and kinda dumb... which I guess is what Metal Gear is all about anyways, but still, at least brush up on some background info.