I got this for Christmas, and I was pretty skeptical going into it, but it has definitely exceeded my expectations by far. I have only played a couple Campaign missions, but it's way better than Reach's campaign, and like someone else said the opening video or whatever it's called was amazing. I was pretty dissappointed that they removed Firefight, but I like Spartan Ops more (even though a few things about it aren't perfect, nothing that matters though).
As for War Games (love the name :lol), I absolutely love the new scoring system! So much funner when the medals aren't just for show/commendations, but I do think they kind of went overboard on them (you get a medal for just about anything you do :unsure). The only complaint I have is that there are so few playlists compared to Reach, but Dominion is an awesome addition. I miss playing games like Headhunter and King of the Hill, basically I miss the playlist Multi-Team where it was 4 teams of 3 where you could choose from a bunch of different game types.
Overall I absolutely love the game and would give it a 9/10 (would've been 10, but there a few other small things that bug me).