Firstly, Google Analytics (GA4) has done away the sessions, page views, conversion rates, and so forth that marketers are familiar with. Some people won’t have a problem with events-based analytics, but most will be frustrated that they have to learn how to do website analytics from scratch.
Google has also made conversion tracking much harder - a strange move considering how important conversion rates are to the success of any business website. You might as well try to go to war with a rival gang, while leaving your fiercest enforcers at home.
Users are also unhappy that the number of acquisition reports has nosedived from 30 in Universal Analytics to just three in GA4.
Custom dimensions are now limited to 50, while you cannot analyze data that is more than 14 months old - a situation that’s far from ideal given the many vital insights that can be garnered by comparing current data with historic campaigns.
Google has also removed many of the features that marketers have long relied on, such as multi-channel funnels and data-driven attribution. Date filtering has also taken a hit, with users no longer able to use hostname filtering to remove most referral spam from their datasets.
There are now also fresh restrictions on IP filtering, with users noting new restrictions on the number of blockable IP addresses. This is particularly frustrating since GA4 doesn’t support Regular Expression, a powerful tool in digital marketing for extracting specific pieces of useful information from large data sets. There's no way out - too many cons of Google Analytics 4!