Canon EOS R full frame mirrorless now includes two camera models... the original 30MP EOS R ($2300, body only) and the soon-to-be-in-stores, just announced 26MP EOS RP ($1300, body only). There are also a lot of rumors of a higher resolution model possibly coming later in 2019... most likely50MP or more and higher priced (essentially a replacement for the EOS 5Ds/5Ds-R DSLRs).

At 440 grams, Canon claims the EOS RP is the lightest full frame mirrorless camera on the market. It's also quite compact... enough so that Canon is offering an "extension grip" for it, to make the camera more comfortable for people with larger hands to use (grip comes in choice of four colors, though the camera itself comes in your choice of black, black or black). The EOS RP uses a small LP-E17 battery and is CIPA rated for around 250 shots per charge.

The EOS R uses larger LP-E6N batteries and is CIPA rated to be able to take 370 shots per charge. However, there is a BG-E22 vertical/battery grip available for the EOS R, which doubles the number of batteries as well as providing secondary controls for more comfortable use of the camera in vertical/portrait orientation.

Battery life is a potential issue with any mirrorless camera. They use an Electronic Viewfinder (EVF) which draws power constantly during use... both for it's LCD screen and because the image sensor needs to be operating and sending it a signal. DSLRs like your D750 get considerably more shots per battery/charge because their optical viewfinders (OVF) don't have similar power usage.

Note that CIPA ratings utilize a fairly tough, standardized method and it's often possible to significantly increase the shots per charge you get with some simple power saving tricks. Users of EOS R have reported typically getting between 600 and 1300 shots per charge, depending upon exactly how the camera is being used and their efforts to conserve power. For example, frequent and extended usage of the rear LCD screen of a camera will drain batteries much faster. Videos also drain batteries faster. And, on cameras equipped with them, using GPS and WiFi both also significantly decrease the shots per charge.

Four lenses were offered initially with the EOS R and are now available in stores:

RF 24-105mm f/4L IS USM ($900)
RF 28-70mm f/2L USM ($3000)
RF 35mm f/1.8 IS STM Macro ($450)
RF 50mm f/1.2L USM ($2100)

Canon has officially confirmed six more RF lenses "coming soon":

RF 85mm F1.2 L USM
RF 85mm F1.2 L USM DS (defocus control for stronger background blur effects)
RF 24-70mm F2.8 L IS USM (note Image Stabilization, which the EF 24-70/2.8L lacks)
RF 15-35mm F2.8 L IS USM (note Image Stabilization, which the EF 16-35/2.8L lacks)
RF 70-200mm F2.8 L IS USM
RF 24-240mm F4-6.3 IS USM (likely a more affordable "walk-around" lens)

Prices and exact release dates for these six new lenses were not given.

It's not official, but there's strong evidence that two more lenses, both telephoto zooms, are in development and may be available later in 2019 or early 2020:

RF 100-400mm f/4.5-5.6L IS USM (likely $2000+)
RF 70-300mm f/4-5.6 IS USM (likely under $1000)

In addition, there are three Canon lens adapters that allow any of the approx. 90 Canon EF and EF-S lenses they currently offer for Canon DSLRs to be used on the R-series cameras. (When used with EF-S lenses, designed for use on APS-C cameras, the cameras will automatically crop to match the lens format.) Legacy EF and EF-S lenses should all be usable too, with these adapters. Canon claims there is no loss of performance using adapted EF/EF-S lenses. The available adapters are:

"Plain" EF/EF-S to RF mount ($99)
Adapter with "control ring", EF/EF-S to RF mount ($199)
Adapter with drop-in circular polarizing filter ($299) or drop-in variable ND filter ($399).

There are also an increasing number of third party lenses and lens adapters starting to be offered for use on EOS R cameras.

You should also look at the Nikon Z-series mirrorless cameras. They offer two models: Z6 (24MP, same as your D750, $2000 body only) and Z7 (42MP, $3400 body only).

There are currently three Z-series lenses offered:

Nikkor Z 24-70mm f/4 S ($1000)
Nikkor Z 35mm f/1.8 S ($850)
Nikkor Z 50mm f/1.8 S ($600)

Officially announced and expected in stores in April are:

Nikkor Z 24-70mm f/2.8 S ($2300)
Nikkor Z 14-30mm f/4 S ($1300)

There is also a Nikon FTZ adapter that allows F-mount lenses to be used on the cameras ($147 if bought separately).

I'm less familiar with the Nikon Z-series cameras, lenses and accessories (I use Canon gear, though not any of their mirrorless yet). I know quite a few more Nikkor Z lenses have been promised in the future. You can find details of those and extensive reviews the Nikon and Canon full frame mirrorless cameras online, as well as comparable Sony cameras and lenses. There's also a Panasonic full frame mirrorless camera coming soon (up to now they've only been producing micro 4/3 models, in a sort of partnership with Olympus).

If money is no object, there's also the Fujifilm GFX medium format mirrorless camera (51MP, $5500) and system of lenses (eight, so far).

For some reason, perhaps from pre-release guessed at specs from various sources, I was under the impression that my EOS R was not as well sealed or as sturdily built as some other Canons, such as my 5DIV. Your statement made me wonder enough that I went to the Canon site to check. I thought the weather sealing and frame were more on a par with the 6D when actually it is closer to the 5DIV in those respects. Just two more reasons why I like the EOS R as much as I do. Getting harder and harder to find anything about it that I don't like!
Thanks!

Good Morning,
Happy Sunday

I wanted to have advice in the following-
I had Nikon D750 which I sent to square trade- because of warranty- camera was totally destroyed, Anyways, I was given the Canon
EOS R System
I wanted to know what you guys think of the camera. I am a photography Manipulation Artist, so for me when I photograph plants and flowers, it’s important to show each details of the life of the plants. If someone can comment, I will be awesome, Grateful for any of you to take the time.