The Canon EOS-RP is widely known as the best deal in a full-frame mirrorless camera. It is also known as one of the most compact and light (485 grams with battery) full-frame cameras. So when it comes to the question of whether it is worthy as a full-frame camera for serious photographers...many have doubts.
The mirrorless EOS RP includes a 26.2 MP CMOS sensor (same as the 6DII sensor), fast and accurate autofocus, 4K video, and the DIGIC 8 processor which is great in low light. It can focus in very low light conditions with the max ISO of 100-40000, expandable to ISO 50 and to 102400.
Among the cons listed against the RP, short battery life and limited 4K video capability are the two main gripes. Another popular gripe is the low frame rate (up to 5 fps). Barring these 3 legitimate gripes, I think the RP is totally worthy of being a full-frame camera for serious photographers.
The RP is loaded with features often found in high-end cameras. To start out with, its Auto-Focus is better than most Canon DSLRs that far exceeds the RP price point, including the 5DIII, 5DSR, and the 7DII that I own. It also has a very good human face and eye-tracking capability which is as good if not better than Sony (I also own Sony cameras). In (AI) Servo mode, the RP actually changes the color of the AF point to signify that it is in focus...a feature missing in all DSLR except the 1D series.
The RP is also loaded with features, some exist only in higher-end DSLRs...these include Interval Timer, Bulb Timer, Anti-Flicker, Multi-Exposure, HDR, ISO auto range, ISO 50.
There are three features that are new that do not exist in Canon DSLRs. These are the new FV mode, the Manual Focus Peaking, and the Focus Bracketing feature.
As a serious amateur photographer equipped with the Canon 5DSR, 5DIII and 7DII, I originally bought the EOS-RP strictly for travel due to its compact size and weight. But I have since grown to love the little camera and barely touch other cameras except for the 5DSR when I need the extra resolution. Most of the cons I can work around without much problem.
Rolling Shutter: I do not shoot while moving so it's not a problem
No Animal Eye Tracking: my DSLRs do not have it either
Limited Silent Shooting Mode: Workaround using 2-shot focus bracketing
Limited 4K Video: I do not shoot videos much and when I do, I use 1080p anyway.
Short Battery Life: I turn off auto-preview, turn on Econ mode which last me about 400 shots per battery. I carry 3 but rarely have to use the second spare.