Still polarizing on GAF, still a great MGS one of my favorite games ever.
For those who love this game, weren't you all disappointed after Act 2? They kept teasing us with slivers of awesome gameplay, but it never materialized.
The final act had an amazing stealth sequence, but that was the only one and then more nonsense cutscenes.
This game was just a huge tease. They refined to the controls to something finally decent, but you really don't get to experiment much since its cutscene city.
I partly agree with you in that they could've had more playtime with this, but it felt like a lot of that was regulated toward MGO2 to extend the playtime in a way, which is why I wish that version had offline elements since before it shutdown. I was disappointed that MGS4 never got a Substance-like expansion, which made games like MGS2 doubly replayable for me. I might imagine an expansion adding 2 or more Acts that acted like Act 1 & 2, more open spaces and chances to test all of your tech.
For what was in-game, Act 3 was decent change of pace from the first two acts, that was fun to replay in different ways (locating the resistance member across the maps while avoiding PMC troops felt a little like The End fight). In replays, I've ended up approaching the whole tailing thing different ways; the most fun might've been trying to take out all the enemies across the maps, and then tail the guy.
Act 4 changed it more by dealing with tech-only bosses at first, but did get better at the Crying Wolf boss fight. And after the Vamp boss battle, the hype of the fighting felt literally palpable, piloting Rex.
Act 5 was shorter than it should've been (at least the stealth part); I would've to cover the ship the same way the tanker in MGS2 was covered. The Screaming Mantis and (especially) the hand-to-hand battle against Ocelot left playing the game on a high note.
But honestly, despite being shorter than some games (certainly MGS3), having the sometimes ridiculous amount of replayability and experimentation is what makes it fun to go back to.
MGS4 is a fantastic game for us hardcore fans. Unfortunately, it must be impossible to enjoy if you're a newcomer to the series.
Despite series like Final Fantasy that change things up in every numbered sequel, it does surprise me when newcomers start with 4 and feel completely lost, at least in understanding the story. In Metal Gear's case, sometimes I think people expect (or prefer) how CoD does it - different mission, probably very little connection to what was before it.