Silent Hill 4 isn't as strong as 2 and 3 but I still think its worth a play. It has its good moments and I kinda dig the whole room thing especially as it changes the further you get in the game. You should be able to pick up the game for dirt cheap these days so I say give it a shot.
SH Origins is fine and plays like the usual SH game and nothing like RE4. I have it on PSP and I think its worth a play as well but its VERY easy and short. I'm talking a bit over 4 hours short. I only paid 10 bucks for it so it was worth it for me but I wouldn't pay more since you'll be done with it quickly.