I have been working at 343 Industries full-time for more than 5 years

Tons of talent at the studio. Very collaborative. Directors and leads are always receptive to everyone's input. Never a shortage of cool ideas going around. Company treats employees well, with good pay and good benefits. More stable than most studios. The Halo universe is chalk full of cool things to work on and be a part of. Never a shortage of awesome things going on.

Cons

Tech and tools are a bit dated, difficult to use, and sometimes limited in what can be done. Once you've ramped up with everything, you'll need the right combination of creativity and technical abilities to build innovative stuff that is taken for granted with other game engines. Quite a bit of ambiguity at the moment, though things are slowly coming together. Some management and production peeps still struggle to grasp what it takes to make AAA games. Feels like a startup company at times, trying to figure out how to produce a game, despite them already shipping Halo 4 and 5. Part of this may be due to that fact they've had a lot of people leave after Halo 5.