I've only finished Act 1 in campaign, but I've got about 15-20 hours in multiplayer, and it's probably the most frustrating of the trilogy.
The Lancer is insanely overpowered, it slows you down, and hits like a truck. The Retro Lancer is difficult to use, but hit's harder than the Lancer. Hammerburst, as always, is nearly useless. Gnasher shotgun is good, but if you're against someone with a sawed off, your up a creek without a paddle, unless they waste their shot.
As for map based weapons, the one shot is hella-fun. Sniper rifle can be awkward to use if your used to not using the scope from GoW1.
Overall, much better than GoW2, but it doesn't have anything on GoW1.
We can put on top hats and monocles and make fun of the English.