It's Call of Duty fighting, Mass Effect shields and health, Diablo 2/WoW item system, head shots kill instantly (mostly, depends on enemy and weapon) and a completely kick *** game. It is nothing like Fallout 3, which had a terrible, terrible FPS system. That was the worst part of that game. Yes, it's fun playing alone. Yes, it's more fun playing split screen with a friend. Yes, it's the most fun playing online with a group of good people. I've already dropped 10-12 hours in the game and am only half way done (doing all side quests and playing with a friend). And thats only halfway done with playthrough 1. Playthrough 2 is a restart with your current level, items, and stats with much tougher enemies and MUCH better loot.
I think soldier is the worst class at least up to level 30. Hunter and Brick (tank) are the strongest right off the bat. I have no experience with the siren (mage). However, I hear that once soldier has enough points to specialize in something (he's a hybrid class, support/infantry/medic) he becomes very strong. I'm playing a 34 hunter right now about to start new game+.
The ONLY bad thing about this game I can find is the vehicle combat, which is only part of 2 quests, and in those quests you don't even have to use them if you don't want to. Instances are tons of fun, the characters are great, it's a very fluid game and engaging game.
America, home of the free gift with purchase.