These are the main problems with the COD series in my opinion.
Short campaign.
OP as fuck weapons that are unlocked WAY too early.
Melee weapons that deal more damage than a fucking high-end laser cannon or light machine gun. (Seriously!? Are the knives and weapon stocks in this universe made out of Tungsten?)
Under powered weapons that for some reason require a higher level than the more OP guns. (Why were the AS14 and Bal-27 starter weapons while the SN6 and ARX were locked away?)
"Merica' fuck yeah" story. (No seriously when did we get to play as a British or Russian soldier outside multiplayer?)
Schizophrenic tone. (The reason why so many people enjoyed WAW and MW2 is that at least they were consistent in terms of tone. Hmm reminds me of two open world franchises that can't make their damn mind on what they want to be. COUGH GTA, COUGH SAINTS ROW).
Overpriced DLC. (How come three maps cost FIFTEEN freaking USD!?)
Cool gadgets and weapons that are only used for a fraction of a mission. (Grapple Hook, Sticky Gloves, Hover Tank, K9 Unit, Juggernaut Suit).
Maps that are either too big (Ghost) or borderline claustrophobic (MW3 and Advanced Warfare).
Mediocre servers.
Terrible community. (I think the only gaming fanbases that are worse would be Sonic and FNAF).