A quick take on the differences in playing philosophy - I don't want to go too in depth so that I can leave plenty of room for discussion.
GK - we know that Reina is probably the best goalkeeping distributor of the ball in the PL, but it seems that he is no longer doing what he did since he came here. Apparently Hodgson wants him to be "more english" which presumably means waiting til everyone is in a set position, before launching a huge hoof downfield.
CB's - too close together, too deep.
FB's - too far from CB's, also too deep.
DM - actually, I'm not altogether sure we play with 2 DM's any more. It seems more like we play with a flat 5, 3 of whom break forwards.
CM - Far too deep, see above.
ST - Isolated, and expected to chase every lost cause, when usually marked 3-1.
Not enough players getting in the box.
Quick fixes.
Push the CB's up slightly
and actually play the formation.
Having 2 sets of midfield (1 defensive, 1 attacking) means we should have at least 2 players between the opposition banks of 4 at all times, thereby creating space for others to join the attack, as these players have to be picked up.
Pushing up the wider players of the 3 attaking mids, means the full backs have to step inside, which in turn creates space for our attacking FB, and also ties up their wide player as he tries to track back.
The DM then supports the flank where the main thrust of the attack is as the wide player comes into the box, doing the job of not only compressing the play, but also of providing cover.
The wide players who go into the box, also support and create space for not only the striker, but also the attacking central player, who in turn creates more space.
The DM not covering for FB takes up a central position to defend against break outs, but also provides a fulcrum to pivot the attack, from one wide area to another.
The CAM also can drop deeper if/when the initial surge fails, to provide support, and spread the play.
These are the basics of 4231, the formation we are supposed to be playing.
What we are really playing is a 451, with no pressing, no movement "between the lines" and total predictability going forwards.