The fighting engine has been polished up and the new story mode is great, but online has balance issues.
Its hard to simulate realistic punching and boxing in a game, but FNC makes a good attempt at it. Mechanics don't take into account sliders and balancing issues, which are reviewed in the Multiplayer section. The punch controls in the game are a big step up from FNR4. Instead of rotating the right stick to punch, all you have to do is flick it. This fluid control scheme allows for much less mistakes and easier combos. Blocking is also streamlined so you don't have to worry about blocking high or low. Movement is fairly realistic for a boxing game and you can use it to effectively cut down the ring or create distance between your opponent just as in a real boxing match. Countering is much harder to time in FNC, and this might be good to some people but bad for others who liked the countering system of FNR4.
Online play is much more fleshed out compared to the last Fight Night. The main online mode is OWC, where you create a custom boxer and fight in the ranks to get a shot at becoming the champion of your weight class. You have a lot of options to customize your boxer, even being able to choose blocking style and punching style. In addition, your custom boxer has skills that you can level up and adds an extra dimension to the game since you can develop boxer builds that match the style of fighting that you want to use.
The OWC mode has some balance issues. It's as if the developers overcompensated for the balance issues of FNR4 that favored close range body punchers and now tweaked the mechanics to favor long range head punchers. Body punches seem to not have any effect on lowering stamina. You will often encounter boxers that fight using a simple but overly effective strategy. All they do is straight punch and pump block. The straight is by far, the most effective punch in the game. Its too accurate and too powerful. In the punch stats seen at the end of the fight, straight accuracy is often higher than jab accuracy. Also, damage is poorly reflected by the physics engine. In an OWC match, I had full health and my opponent hit me with a power straight and flash knockdowned me. In the slow-motion replay the punch glanced off my cheek.
Story Mode is the one of the best new features in FNC and serves as a good appetizer to the game. The plot and dramatic music makes fights feel cinematic. You will be put in different scenarios such as a fight where you can't use body punches or a fight where your opponent has an extremely powerful hook. Beating these scenarios is pretty satisfying and if you don't mind the A.I. issues, will put up just enough of a challenge to keep you hooked but not frustrate you.
I like to build my skills and have fun in the singleplayer modes of games. In FNR4, the A.I. was challenging enough that I got a lot better just from playing legacy mode a.k.a. career mode. In FNC, the A.I. could have been pretty good, but it doesn't manage it's stamina well. Unlike previous Fight Nights, the lower the stamina, the easier it is to get stunned or knocked out. The A.I. doesn't take this into account and will throw punches even when stamina is low, leaving itself open for an easy knockout.
Legacy mode has taken a step backwards. Although the Legacy Mode in FNR4 was pretty simplistic, the stat progression system was more realistic and the interface was intuitive. In FNC, they overhauled the Legacy mode such that it's extremely easy to level up and get a boxer rating of 90+ while facing boxers in the ratings of the 70 - 80. Also, the new interface is unpolished, hard to navigate, and a lot of the training options/minigames don't make sense and are useless. For example, in a training week, you can choose to do "Athletic Training" instead of "Skill Training", but "Athletic Training" only provides temporary stat boosts so it's useless and just serves to confuse the player.