Assuming you are getting a relatively new device (and not something from the Viet Nam era or the first Desert Storm):
Generally very good to excellent. Bright stars will halo. How much depends upon the halo rating of the tube. But note this is not a measure of resolution - it is the detector being saturated by that star. What you want to look at are the stars of mid-range or fainter. Preferably fainter. These should be pin-point.
A month ago there was a thread on the Eyepieces forum where the usual NV haters made the usual claims that NV devices "lack resolution". I decided to do an empirical experiment by printing a standard eye chart, and using my NVD to read it. Results: At the proscribed distance of 10 feet I had no difficulties reading from the 20/20 line.
The ability to read the lines was dependent upon illumination - just like normal vision! Not surprising since the final link in that chain was a human eyeball.
As far as compared to a conventional eyepiece, if you have manual gain you can make this so by turning down the gain on the intensifier. My device is white phosphor, and I can make it dim enough it is difficult to differentiate from my Meade 26mm Plossl. But why? Makes as much sense as buying a 20" Dob and masking it down to 4".
If you think that AFOV is the primary function and defining performance measure of an eyepiece, you will not like NV. AFOV on most devices is 40 degrees.
Averted Vision and Dynamic Range
One can use averted vision with NV. However, why? Just like getting a larger scope, the idea is to make the Faint Bright. Averted Vision is the ultimate in low resolution vision! Your goal in any situation should be to use direct vision so as to realize the full resolution of your eye. Averted vision should be the tool of last resort for the dimmest targets.
The other part of your question deals with dynamic range. No device - film, digital, NV - made by man has the dynamic range of the eye. That is a fact of life.
But it does open up possibilities. For example, this time of year a popular observing challenge is the HorseHead nebula. I don't know your experience level, but suffice it to say many boxes need to be checked for a chance at success - such as excluding 2nd magnitude Alnitak from the field of view. While your eye has excellent dynamic range, it can't take it all in at the same time. Alnitak will overwhelm the nebula.
With a NVD this is not a concern. In fact, the NV astronomer can frame a nice view with the HorseHead, Alnitak, and the Flame Nebula.
And we can do it from the city on any clear night with ridiculously small apertures. All direct vision.
One final note - Good thing you stopped here first, as opposed to the Eyepiece Forum. There are a number of people there who do not like the technology - which is fine. Unfortunately, they cross the line by posing as "experts" offering their opinion as facts.
Should you find these people, please do ask them if they have ever owned a NVD. If not, get the details from them on the (usually) one time they looked through one. How long ago? What objects did you look at? What device was it? What was the focal ratio of the system? What filter was used? Did you adjust the diopter or gain settings?