For those who have never played an MG/MGS:
1) Yes, you can play this without skipping anything and "get" the story. You may be confused as hell. You may think it's over the top. You may actually enjoy it for any of the several ways I understand it to be enjoyed (my way of enjoying it isn't the only one I'm sure). There's about 6 hours (that's 3 movies) worth of expository story performed by top professional voice actors and excellent motion capture for the animations. The timing during dialog could be tighter almost everywhere, but I've never seen a game get that right yet, so I won't ding MGS4 too much for it. The action scenes are stellar. Having played the former games only serves as an indicator that you've already experienced this sort of thing before and weren't totally turned off by it. And if all else fails, there is the MGDB on PSN.
2) Don't Panic. You can also skip almost every cut scene and bypass 95% of the story (this is true for all the MG/MGS games in my experience) and experience 5-20 hours, depending on how fast you are replaying, of very exciting stealth action with an astronomical replay value due to a built-in achievements system. In fact, many fans like myself do option 1 first, then option 2 several times to complete the achievements. That 5 hour figure is _the_most_brutal_and_speedy_path_, not an indication of how much content is actually there.
3) The second to last scene will demonstrate to you what interactive fiction is meant to be, in my opinion. When you understand the term, "tunnel crawl", you will know what I mean. I almost cried. Twice. I'd put it up there with what happens to Aerith in FFVII on the scale of evoked emotional response from a video game. Truly, a peak moment for the craft.
4) If you are averse to risk, rent it, and savor/lament having to return it (or rerent) before your 3rd speed/stealth/extreme run is complete. If you have any hide at all, buy it; it's a keeper and an instant classic.
I hope this helps those who want spoiler-free, concrete justification for calling this a must-see game.