Halo 4 isn't bad at all, it's actually pretty good, however it's also without a doubt the worst Halo game ever.
I've only played around 5 hours of the MP so far and it's a ton of fun. It's got some fantastic new ideas while retaining the classic feel of Halo. I can see myself putting a lot of time into it over the coming months. Just awesome.
The campaign on the other hand is Halo 2 all over again, all day long, but worse. Linear, short, boring, and dragged down by an awful, weightless story. The great dramatic stuff from promotional like material like FUD doesn't translate to the actual game at all. The level design is a series of long, narrow staight lines, that expand every now and again into slightly more open areas. The music, while not bad unto itself, is used extremely poorly throughout the campaign. It's dull, monotonous and curiously absent whenever it's needed most. It doesn't sound like Halo at all and most of the time I wanted to turn it off. Microsoft, whatever you need to do, however much money or sweet talking it takes, you need to get Marty O'Donnell working on Halo 5. The new weapon sounds mostly suck IMO (though a couple of them are meaty and awesome). The graphics have some nasty pop in in certain areas, and Master Chief's FOV is awful (MP looks much better without the Metroid Prime visor). Also I'm pretty sure the main villain is
, or at least that was what kept going through my head every time somebody said his name.
Spartan Ops is no replacement for Firefight mode.