GA4 is not "the old Google Analytics with a new interface". It is a different way of recording what happens on your site, and this difference changes both how it is configured and how it is read.
Why GA4 is different from Universal Analytics
The old Analytics organized data around the session: how many sessions, how many pageviews per session, where they came from. GA4 organizes everything around the event: every action, from loading a page to clicking a button, is an event with associated parameters. Sessions still exist as a concept, but they are reconstructed from events, not the other way around.
The advantage is that you can measure granular actions (a scroll, a download, a video view time) without having to set up complex custom events as you did before. The disadvantage is that, if you do not correctly configure which events count as conversions, the main GA4 reports remain generic and not very useful for making decisions.
The minimum concepts to find your way: events, conversions, audiences
An event is any recorded interaction: page_view, click, scroll, purchase. A conversion (called "key event" in GA4) is an event you have decided is important for the business, such as a purchase or a form submission. An audience is a group of users defined by rules, for example "people who visited the pricing page but did not buy", useful both for analysis and for advertising retargeting.
The three reports I look at first
- Traffic acquisition: where visits really come from (channel, campaign, source), to understand whether the advertising budget is bringing the right people.
- Conversion path: which pages and channels contribute before a purchase or a lead, not just the last click before the conversion.
- Engagement by page: which pages hold people and which lose them, useful to understand where to intervene even before changing the campaigns.
The most common, and most costly, configuration mistakes
The most frequent is marking as a "key event" something that does not represent real value for the business, such as a simple page view instead of a completed purchase: this artificially inflates conversion numbers and leads to wrong decisions about which campaigns work. The second common mistake is double counting of conversions, for example when the same purchase event is recorded both by the main tag and by a duplicate tag installed by mistake.
The third, more subtle, is not linking GA4 correctly to Google Ads: without this link, conversion data does not flow back into the advertising platform, which therefore optimizes campaigns without really knowing what works.
GA4 alone is not enough: what to add for reliable data
With the blocking of third-party cookies and increasingly restrictive browser privacy settings, GA4 alone loses visibility on a growing share of traffic. For this reason, on projects with significant advertising budgets, I always add server-side tracking, which recovers part of this missing data while respecting user consent through Consent Mode.