I've installed just now Ultima 9 and i'm a little bit disoriented by this things: why gog choose to make us use glide and not Direct3d directx 7?
I've tryed the game in glide version 1680x1050 4:3 ratio and it's awful. With direct 3d (forcing 4:3 ratio by nvidia pannel) it's wonderful. I'm reading that the game give some problems if it's not running at 30fps and glide provide this amount, but there are more reasons to run it in glide mode? I mean serious reason that i don't know.

There are some glitches or bugs that prevent you to finisch the game using direct3d that you can avoid using glide?

edit:
obviously i'm using updated glide and 1.19h

I can't speak for this game.

But in general during that era of gaming. The glide versions usually offered bells and whistles including a better color pallete, better transparencies, better water effects (transparencies/reflective) or dynamic reflective surfaces (marble floors that reflect characters on screen for example), multi-layered transparent skyboxes (allowing scrolling clouds, lens flares, floating sun, or fog layers), improved color lighting, lamp halos and shadow effects. 16bit to 24 bit rendering effects.

This could be seen particularly with Unreal 1 games.

Sometimes depending on the engine glide originally offered higher resolution than direct x allowed (but ironically ya through patches its easier to force direct x into higher resolutions).

One has to realize in 1999-2001 era. The 3DFX Voodoo Glide API was the top of the graphics card technology, it offered special effects that no other card could handle. Directx wasn't designed to access those abilities, and most cards couldn't do what the glide cards could do.

http://www.1up.com/do/blogEntry?bId=9091474

https://www.youtube.com/watch?v=zqdeyseQAP4

I understand what you are telling. In the past i had a vodoo1 and 3, and they works great for example with Jedi Knight. Jedi Knight with a Riva Tnt2 card or with a Geforce is worst that with the Glide.
But when Ultima9 come out there were already in the market a lot of geforce card. Maybe now, and i'm telling now, the results playing with Ultima 9 in glide is awful because of some lacks in the glide emulator.

Anyway, basically now i have to choose in wich way to play the game, and i'm asking if there are some precise reasons to choose glide, some reasons related to bugs or glitches that you could meet playing with direct3d.

Ultima 9 came out in 1999.

Deus Ex came out in 2000. It also originally used Glide's graphics bells and whistles that other cards couldn't access using dirext3d or openGL modes.

Undying came out in 2001. That game also Glide's graphics bells and whistles, which direct3d couldn't mimic.

But those were both Unreal 1 based and thus were designed with glide in mind. The companies didn't bother to make special drivers for Nvidia cards.

Direct3D support lacked all the features (see screenshots I posted).

Some fans have made fan direct3d render that remapped the old glide graphic calls to direct3d 10 graphic features to get similar or improved graphic effects on some Unreal 1 games.
http://kentie.net/article/d3d10drv/

Ultima 9 has its own engine though, designed specifically for that game. I don't know if all the drivers direct3d and glide were designed to have same graphics styles, or if they went out of their way to focus on glide only (like Unreal engine games did).

Glide was apparently technically superior to to the TNT cards and limitations of direct3d at the time in some ways. But some companies still didn't take advantage of the 32 bit image quality and chose to utilize special features that glide offered instead. Or rather they may have offered 32 bit version of the game, Undying does for example But the glide supported features make the game more atmospheric. They didn't go out of their way to simulate same glide special effects on TNT2 or similar cards at the time.

Still it took a while for Nvidia to catch on to both gamers and designers. Which is why I still warn about games in that early 1998-2002 period tending to lean towards Glide API over any others.

The reason why gog sets it to use a glidewrapper is to ensure maximum compatibility, Direct3D is dependent on specific DirectX functions and old Direct3D games cause a lot of problems with newer hardware.
But if you really want to try Direct3D it is probably possible to make it so, although I don't know for this game as I don't own it.

The problem i have with Glide is that U9 runs slooow with it. With D3D it runs smooth, but the top of the journal is cut off and the spellbook covers the toolbelt so i can't drag spells on it.

EDIT: nglide 1.01 was the problem. The performance goes down when i use it. I do not know why.

Has anyone managed to get this GOG version running properly in widescreen? Glide version works but only if the game runs in 4:3 box within my 16:9 screen. There is a WSGF article showing how to hex edit the u9.exe and add horizontal FOV so the game is correct aspect when choosing a resolution like 1080p. But for me, it looks weird and stretched still. It "changes" the FOV to be different looking, but not correct aspect as the screenshots indicate on that article. Are people using D3D version in their GOG release and does it actually run? If I try D3D it just simple has errors on launch and crashes. Only Glide version works and seems the widescreen hex editing hack doesn't work correctly on it.
Or are people seriously just playing this game via 4:3 ratio in this day and age and are fine with that?

When I played it, I had a 4:3 monitor, so it wasn't much of an issue! That's what it's designed for, so I don't think you're getting any benefit out of seeing more of the view unless the black side bars just bother you that much.