I just finished it last night.
Pros:
-Its the most fun to play out of the entire series.
-cut down on the annoying interactive cutscenes.
-More generous with ammo and healing items than the entire series.
-Co-op (even in mercenaries)
-Nice array of weaponry all but 2 can be found without having to be purchased.
-Use of classic monsters and weapons.
-No more type writers.
-The boss fights are amazing
Cons:
-AI partner is bearable. Its better than most AI at fighting, healing you, and what not. But it has no common sense and you have to give it commands during crucial situations. This was meant to be a 2 player game.
-There is a severe lack of puzzles
-Its not really scary, I guess the lack of low ammo situations and limited save points take all the stress out of the game which caused most of the fear.
-The ending kinda sucked.
-The weapon upgrading is a lot more watered down from the previous installment.
-The treasures are watered down, just find and sell, no piecing together anything.
Overall, This game is bad ass. Its a lot of fun to play if you have someone else to play it with. Its the best game in the series as far as gameplay, 4 Still has the best story.