I initially liked the SP part of the game when it came out, but they screwed everything up so bad for the first year after release that I never bothered to go back. Still can't bring myself to get back into it. Mostly the missions were terrible. Always exactly the same. Just a bunch of bullet sponge guys to kill wave after wave of. They really needed to add some random branches and events to the missions to keep them more fresh.
The Dark Zone was a mess of hackers and griefers, and while it could be fun for a little while, you'd eventually run into those guys and then it would suck. The level ranges for the zones were too wide as well, as you could end up against people with FAR better gear who would annihilate you in seconds. Oh, and gear balance was shit too.
Overall, they did a shit job on the game with everything but the visuals, and then they spent the next couple of years trying to fix it all, and basically getting it to where it should have been at release.
"The whole problem with the world is that fools and fanatics are always so certain of themselves, but wiser people so full of doubts." -- Bertrand Russell (I think...)