I know it sounds crazy probably but... damn it I have no other way of explaining my pure joy for this game. To be fair I hated it to begin with. In fact I thought about breaking the disc because of some frustration of bad game mechanics. The difference is I found myself playing it for 8 hours straight last night on professional and then played some multiplayer with 2 friends and I learned that I love this game.
Anyway if you already know this stuff good but for me and most of my friends it took someone telling us to figure it out.
- Melee specials - Each character has a melee special move. The basic melee is just the melee attack, if you press the interact button during the attack you will do a finishing move, though this leaves you open to attack. The best move though for tactical purposes is the special melee which is done by attacking then pressing the special ability button ( Y on default XB360 control) after an attack. So the medic will grow a herb out of an enemies chest making it so you can heal up your team, or if you are the field scientist you can inject the enemy and then they become infectious zombies that ONLY attack enemies. This is especially effective when there is no zombies and only spec ops.
- Use Bertha's injection to run past tough levels. One of Bertha's injections can negate %90 damage for a couple seconds. When ever a level go too tough I would inject myself with it and then run to the next checkpoint and then die possibly so my entire team might restart from that check point. In fact I skipped most of the entire last mission by just running past all the enemies and jumping into the next area causing a cutscene. This only works on missions that don't have blockades or require you kill an enemy before advancing but there is a good chunk of these get to the checkpoint missions. Also use this ability when team mates go down. Even when your bleeding and surrounded by zombies they barely scratch you. FYI I think it might work with invincibility of lupo but i haven't tested it yet.
I'll post more tips when I get back from work but how about everyone here post tricks they have learned :]