Good first
I really like the game mechanics in general, weapons feel clean, shots register great, and most of the new weapons are fun and bring some freshness to halo. If I could choose anything to be good in a game it would be the mechanics because that gives a game potential.
Well that was a short good list
Now the bad
First and probably most painful are the maps Why are they so BIG! I really don't enjoy any of the maps and find myself not even excited to play any of them. In some of the 4v4 playlist a map can be dead silent for a good minute without players finding anyone from the opposing team. It also makes most the guns like scattershot, shotgun, incineration cannon, and sword useless because most your battles will be long range with the DMR, BR or snipe. They only have one BTB playlist and didn't even make a sniper playlist at launch so why the big maps!
Next is the re spawn system. You should not be able to re spawn instantly like you can in most the playlist. It totally ruins the flow of the game and makes me not even care about dying because I feel there is no big penalty for it. You also can't keep track of who is where because players are constantly re spawning all over the map and can even spawn right in front of your sights. They've also taken out any indication of where your teammate died, which used to be the letter X in red, this makes it even more difficult to call out enemy positions to your teammates and the whereabouts of the opposing team on these BIG MAPS!!!!
And finally scoring/medals. I DESPISE the new scoring and I really didn't think it would bother me that much but it does. Halo has and always should be counted in kills, not points for getting head shots or assists. If you kill a player it should be just that, ONE single kill.
The medals are dull and boring. I would get so pumped when I got multi kills in other Halos and see those BIG and COLORFUL medals pop up on screen. In 4 you can barely tell if you get a multikill because the medal is a tiny black circle. Another gripe with medal is that there are too many of them. You seriously get a medal for anything you do and I mean ANYTHING. This takes away any sense of achievement because you are constantly getting a medal every time you kill a player.