I've been playing through Downpour for the past couple of weeks. You should know that I came into the Silent Hill community pretty late (around Origins) and I have only recently retroactively played though the original three games (I still haven't gotten around to
The Room). And frankly, I think that more recent titles in the franchise are better than those ones. I've enjoyed Shattered Memories more than any other title in the series and Downpour is a close second for me.
If you are familiar with the Wii title, Downpour takes many elements from it and adapts them to suit the new character. In Shattered Memories, Silent Hill was blanketed in snow and it would freeze over when you entered the other world. Downpour uses rain to sort of the same effect, making it dangerous to be outside during a rain storm. Also taken from the previous game is the chase sequences, although you won't be running from fleshlings, they've been replaced with an ominous dark presence that seemingly wants to consume your character but they more or less play the same.
What's changed is that combat and exploration makes a return to the series. Combat is made more difficuly by having only one melee weapon at a time and they're only good for several enemies before breaking apart. The protagonist isn't as competent a fighter as the character from Homecomings and this helps make enemy encounters feel more dangerous. Fighting off one or two enemies is usually easy enough but when they have larger numbers (usually during a rain storm) it's more advisable to simply run away. Also, the game is probably the least linear one since the original titles, you'll have to do some honest exploring to find things and the addition of side quests is definately welcome.
The game suffers from some technical issues like texture pop-in but most jarring is the framerate hiccups. No deal breakers but it does manage to give the game an unpolished feeling. A patch has finally been dated for both PS3 & 360 (right as I'm reaching the end of the game no less) so don't let that put you off. Downpour is definately a return to form for the series and it's played closer to a traditional survival horror game than anything else this generation. Honestly, I can't recommend it highly enough.