I've played through the main campaign and completed it using the Sam B character.

I enjoyed it more towards the end, the jungle and lab area was probably the best part of the game. I started playing the Ryder White DLC and quit about an hour in. Though the gameplay's the same, the levels have some game affecting bugs that the main game didn't. There's a part where you have to go through the sewers again, which have a /lot/ of the infected present. Unfortunately they seem to respawn while you're still in the area and end up swamping you with barely any respite. The glitch that made me quit was while walking through a narrow area I found a thug, so was about to run in with sharp things swinging when 4 infected spawned out of nowhere literally right in front of me. I've never liked respawning enemies in games like this, and to do it so blatantly is a mahoosive faux pas. 

The DLC was ok but didn't really add anything to the main campaign. I've played through DI and DIR a couple of times, now I've got Sam B basically maxed out with all the best ("gold") modded weapons and $$$ (3M and counting ATM), I just roam all over the map killing zombies at will. It's best to attack hordes with explosives (the sonic grenade is the most effective) before they even see you, firearms are very effective at medium-close range against all comers especially when modded with fire/shocks, and the auto sniper-rifle at a distance. The melee weapons are the most fun and can be effective against hordes provided you don't let yourself get surrounded, and have space to back up. Oh yeah, indoors (warehouses, basements etc) where you are more likely to encounter mixed hordes of zombies, thugs and worse, you can kill many through the bars with firearms, open doors and toss in grenades and molotovs then close the door. Always carry huge supplies of explosives.