I don't think Halo 4 sucks at all, but I'll tell you what I dislike about it.
- The level and mission designs of later campaign missions, IMO, were as boring and repetitive as the initial Spartan Op missions. Kill these 3 Forerunner orbs. Good. Press 50 buttons. Great. Kill more orbs. Do all of this while fighting through bullet sponge Prometheans.
- Customization was lacking, and Forge was a step back versus a step forward (it's better now).
- Though I LOVE multiplayer modes like SWAT, Big Team Slayer, and Infinite Slayer ... I'm personally not having the fun I use to have. I'm not into the multiplayer as much I use to be, and I don't think it's losing interest in Halo multiplayer. If Halo 1 was online, I'm pretty sure I'd be playing that all the time.
I really want a bigger scope multiplayer to exist, like what Battlefield 4 for the PC offers. I think seeing a large scale Halo multiplayer would be amazing, and it makes sense. Halo is known for its giant epic battles. I'd like to be able to always participate in one.