Played from Wave 1 to Wave 20 on Hardcore all of this afternoon with a friend. If you want to be effective in Horde mode, do it on Blood Drive, bunk down in a really narrow corridor, kill a mauler and block the corridor off with a sheild. Then just use your Lancer or SNUB on all the crap that gets stuck behind it. Pick the sheild up and move it in the lulls so you and your buddy can get ammo. Also, a shield with a Mulcher on top in a 2m wide corridor is a wonderful spectacle, As for poison grenades, Chac, use them on Boomers and Bloodmounts on Horde. Trap em somewhere and toss a poison in there with it, works wonders. Poisons also work really well when you tag people with them. The Bloodmount has to be the toughest, most annoying enemy in any game, ever. And thank god for full Bot support in multiplayer. Genius move.
As for the story, I really liked it and I thought that the part with Dom's wife was ok, but it really should have come much later in the game.
SPOILERS AHEAD. HIGHLIGHT TO READ.
I think that the Sires are probably an early form of Locust, and that most of the locust (excluding crap like Corpsers) are POWs from the Pendulum wars. Adam Fenix probably knew this as well. I reckon the whole Locust race was probably meant to be a new weapon in the Pendulum Wars. Except, it either got out of control, or it is being used exactly as planned. I think the Queen was also a human scientist or something.
But we shall see, won't we?
The game is absolutely superb, by far the best FPS I've ever played. Meatflag forever.