Camera shopping has a similar trap to smartphone shopping — megapixels get the marketing spotlight, but sensor size explains most of what actually differs between cameras in price, size, and image quality.
Sensor sizes, to scale
A larger sensor captures more light per pixel, which generally means better performance in low light, smoother gradations of color and tone, and more control over depth of field (how blurred the background looks behind a subject). That's the main reason a full-frame camera costs more and is physically bigger than an APS-C or Micro Four Thirds camera — the sensor itself, and the lenses built to cover it, are simply larger.
None of this makes smaller-sensor cameras bad — Micro Four Thirds and APS-C systems are dramatically more compact and often cheaper for a similar level of control, and are genuinely excellent for travel, everyday shooting, and most casual to enthusiast use. Full frame earns its size and cost mainly in specific situations: challenging low light, professional portrait work relying on background blur, and large prints where maximum detail matters.
Megapixels stop mattering sooner than expected
Beyond roughly 20–24 megapixels, additional resolution mostly helps with large prints or aggressive cropping after the fact — it does very little for how a photo looks on a phone or computer screen, or in a normal-sized print. A camera with a larger sensor and fewer megapixels will often outperform a smaller-sensor camera with more megapixels in actual image quality, especially in anything other than bright, ideal light.
The lens matters as much as the body
A camera body is only half the system — the lens attached to it has just as much influence on sharpness, low-light performance, and background blur as the sensor does. It's worth budgeting for at least one good lens rather than putting the entire budget into the camera body and settling for whatever kit lens comes bundled with it.
The one thing people forget
Check what lens mount the camera uses and whether that mount has a healthy range of lenses available, including from third-party makers — not just from the camera's own manufacturer. A camera system with a limited or discontinued lens mount can leave you stuck years later when you want to upgrade or add a new lens.