Please note that the following is my opinion and hold no validity. I have been playing Reach for over a year now across multiple accounts whenever I had the time and so far this is what I have come up with.
The Good:
Multiple Abilities within the game make it so almost could anyone can play the game and do well.
The new game types (including the action sack variants)could allow the game to be replayed over and over again.Plus, the customizations add to the selection could make it so no gametypes are almost never the same.
Invasion possibly one of the best gametypes ever made.
Firefight option make itto where you can blow the hell out of the covenant or be slaughtered by them.
The Bad (sadly):
The Abilities are stale and sadly you will only use maybe 1 or two most of the time.
The voting system makes it so you almost always play the same maps over and over again.
Custom games are almost never played because while the options are many there are alot of problem (IE Active camo even as a power up or starting off ((and not AA)) wears off with movement).
The elites have a huge hitbox and are rarely ever played as.
Invasion only has three maps (including dlc) and sadly boneyard has been overplayed.
DLC is practically useless because the chances of you actually running into the set amount of players having it is near to none.
Firefight has host and connection problems and even when you have the best connection you will still lag (Same with campaign).
You can skip literately most of the campaign.The only levels where you can’t quickly run through it is New Alexandria and Long Night of Solace.
In all honesty this is what I have noticed.