I also recall the early days of D3D (Immediate mode), which although it came after OpenGL, immediate mode allowed better integration with the cards at the time (notably 3dfx) and OpenGL did not have hardware drivers, which meant it was limited to software rendering. So, if you were into game dev, then D3D was your only option early on.
My recollection was that it wasn't until NVidia started up (and broke 3dfx by poaching engineers) that OpenGL started to become 'better'. Intel was left in the dust until mobo support for DMA (?around DX5?), which allowed cards to gain quick access to RAM, which was vital for texturing (you always had to 'upload' textures to the card itself prior to that). It was the final nail in the coffin for 3fdx at that point, who still hadn't released a new card for ages, and OpenGL was finally on par with D3D. D3D had a retained mode which began to be really useful by about that time too.
At the time, many people wanted to use OpenGL because it was loads easier than Immediate Mode and a lot more intuitive to grok. I recall a certain prominant Doom developer berating D3D loudly in a private email list (John Cormack) about this very fact. Ironically, a few months later some guys released a demo for a game called "Unreal" using D3D and everyone was blown away. (circa 1995-6). More ironically, it wasn't for another year that GL Quake came to fruition.
Carmack loved OpenGL because GPU vendors could (and would) release propriety extensions that exposed all the new functionality of new GPUs.
He would rewrite custom rendering paths for various GPUs and common sets of extensions, allowing him to improve performance and/or improve graphics.
With Direct3D, Microsoft defines a common feature set that all GPUs supporting that version of Direct3D are required to support, and any extra functionality that GPUs might provide on top of that are locked away, completely inaccessible.
Checking the Doom 3 source code, he the main ARB and ARB2 pixel shaders paths (equivalent to dx8 shaders). Then for the older gpus that mostly support pixel shaders but not in a standards compliant way, he has an nv10 code path and a nv20 code path.
Then he has a r200 code path, which I think just improves performance on r200 graphics cards over regular ARB2.
Extensions are a good thing since it allows developers to take advantage of new functionality and provide it to consumers pretty much immediately - this is a win win for everyone involved, programmers use cutting edge functionality and consumers actually get to use the fancy GPUs they paid money for.
Direct3D programmers disliking extensions make me think of the sour grapes fable.
But OpenGL providing extensions doesn't mean that Direct3D programmers are free of having to implement different code paths - if anything during the 90s with the proliferation of 3D cards and different capabilities flags, programmers had to take into account a lot of different possibilities in their rendering code (and most failed to do that with games having visual glitches everywhere).
I don't like the term "poaching". It implies that the engineers who took better paying jobs did something wrong, whereas they were just trying to retain a bigger portion of the enormous value that they were creating.
My recollection was that it wasn't until NVidia started up (and broke 3dfx by poaching engineers) that OpenGL started to become 'better'. Intel was left in the dust until mobo support for DMA (?around DX5?), which allowed cards to gain quick access to RAM, which was vital for texturing (you always had to 'upload' textures to the card itself prior to that). It was the final nail in the coffin for 3fdx at that point, who still hadn't released a new card for ages, and OpenGL was finally on par with D3D. D3D had a retained mode which began to be really useful by about that time too.
At the time, many people wanted to use OpenGL because it was loads easier than Immediate Mode and a lot more intuitive to grok. I recall a certain prominant Doom developer berating D3D loudly in a private email list (John Cormack) about this very fact. Ironically, a few months later some guys released a demo for a game called "Unreal" using D3D and everyone was blown away. (circa 1995-6). More ironically, it wasn't for another year that GL Quake came to fruition.