I'm thinking about taking the plunge and for the first time, play the (main) TES series. I already have Skyrim on Steam which I hadn't played yet and after getting Arena and Daggerfall with Quake I went "fuck it, maybe I should buy Morrowind and Oblivion and play it from start to finish?".

Although I appreciate mods I prefer to play games as they are with all their flaws (not glitches, of course), so would MW run on WIN 10, widescreen without any special mods ?

Morrowind doesn't support widescreen without mods, but the game should run just fine on Windows 10.

One way of getting widescreen support:
[url=http://pcgamingwiki.com/wiki/The_Elder_Scrolls_III:_Morrowind#Widescreen_resolution]http://pcgamingwiki.com/wiki/The_Elder_Scrolls_III:_Morrowind#Widescreen_resolution[/url]

Morrowind works fine for me at 1024x768 resolution, without mods.

Of note is that I am playing it on Linux via WINE.

Do note that the game does have bugs and I do see it crash once in a while, so save early and often. (This is a good idea when playing any Bethesda game, in fact, and a good practice to get in the habit of.)

Tell me about it...

I'm currently playing Fallout 3 for the first time and is is a clusterfuck of bugs and crashes, especialy on WIN 10.

Morrowind runs fine on my Win10 PC and doesn't require any additional patches or mods (in addition to those provided with the GOG version). My native monitor resolution is 1680x1050 (16:10), game resolution 1280x960 (4:3).

Start the launcher, go into Options, and see what resolutions you are offered (depends on your graphics card, I guess). I was offered 4:3 resolutions only, and chose the largest one on the list.

I have Morrowind installed on an older PC connected to a 4:3 monitor and use the same game resolution there - not much of a difference, as far as I can tell. There must a small distortion on my 1680x1050 monitor (as there are no black borders), but it's not or hardly noticeable for me.
Bear in mind that Morrowind plays in a fantasy world and most inhabitants look "odd" anyway. A small additional stretching may be noticeable for people who are used to playing the game on a 4:3 monitor, but when it's your first playthrough, you wouldn't be able to tell the difference.

Bottomline for me would be to give it a try.