Lots of hardcore fans disliked how the devs shook up the core Halo gameplay with some questionable additions.
For an in-depth critical look at the Halo games, I highly Lucas Raycevick's Halo Dissection documentary series. It provides very interesting retrospective views on the games from a gameplay, lore and even development standpoint.
(Seriously, every Halo fan should watch these. They're by far some of the most top-quality-yet-underappreciated videos I've ever seen in the Halo community. It's probably best to watch the series from the beginning.)