Well, you still have to do ch.3 first part which is slow and on the game's time not yours. Then you have to do the 2nd half of ch.3 which again you have to play it on the game's time until the game says it's time to move on. Both these parts were fun the first time but not so much on replays. Ch.4 just isn't that fun to replay because it's dull. Ch.5's final fight is a chore.
Do you also hate the Sorrow 'battle'? or how about the latter? having slow moody sections aren't new to the series, it just seems a lot more jarring because the first two acts have the most action seen in a Metal Gear game.
The 4th and 5th acts a bit dull to replay, especially the 5th because it doesn't have that MGS1 nostalgia there, but I did like them the first time I played. First two acts are amazing and I've replayed them a couple times.
I can only hope that there is a MGSPO type game made for the PS3/360/PC/anythingbutthewii that has the MGS4 gameplay and is purely combat situations and all that. Portable Ops was a good game outside of the controls issues.
And I want AC!D 3 on PSN/XBLA/Steam/notwiiware