I can't really compare it to CoD because I only played World and War and that whole 1-shot-1-kill garbage was a complete mess and nightmare.
In that respect, Halo 4 is very fun on multiplayer. There is a ranking system that you level up based on if your team won and if you stuck through the round. It isn't a fair representative on the quality of the person playing the game, but it does even out a lot of things to make everything more accessible and for everyone to have a fair advantage of everything. There are about a dozen maps (some larger than others) and some include vehicular warfare.
To top it off, you get 6 loadouts and each loadout has certain weapons/skills/ordinances that can be unlocked later in the game (i.e. more stamina, quicker reload, jet packs, more ammunition to primary weapons/ordinance dropped weapons). There are also skins (armors) you can unlock as well as emblems customizable to color.
To top it off, there are a SLEW of challenges (daily, weekly, monthly) to accomplish for more xp (don't necessarily know if there are unlockables just yet).
You do have stats that are saved in the Waypoint system where you can check your progress and anyone else. The community is good. On the battleground, it really does show who is experienced/inexperienced by the player's actions. (take for instance, you'll see some people running over there own teammates or getting stuck in walls while flying).
The multiplayer isn't difficult, it is just really about adaptability.
Just one thing: don't let your k/d disappoint you if it gets low. When I first played the game it was at .27 but slowly rose .63 in a couple of days of casual play. It's real run though.