(This post is pretty long, so I’m breaking it up into sections separated by tildes.)
First, I think that you’re right in saying that you haven’t had an answer comparing C4 and Panda.
I suspect that the reason for this is simply that this forum is fairly small and largely populated by people who have chosen Panda as their development engine: people with experience using C4 are likely to be relatively few here.
On top of that, I’m not sure of how widespread the use of C4 is – if you had asked for a comparison with Unity, for example, you might have had better results.
Have you tried asking your questions on a larger, more general forum? If not, perhaps do so – GameDev.net might be a good place to start.
(On that note, if I may ask a side-question, why do you choose C4 in particular?)
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As to your specific points:
I’ll note that I don’t think that I’ve used C4 myself, but might nevertheless have something to add:
1) General Game Quality/ability
Here I think that I agree in part with both you and those who have replied to you: I think that in some cases one engine might either aid or impede development more than another; for example, one can make a platformer in Adeventure Game Studio, but I imagine that it’s rather harder than making an adventure game.
That said, for a fairly general game engine like Panda or Unity the quality of the final game likely depends rather more on the skill, patience and perseverance of the developer than on the engine itself. There are likely exceptions one way or the other – very poor engines impeding development, or particularly good ones aiding it – but I’ve seen good games come out of poor engines and poor games coming out of good ones, I do believe.
2) video quality & shader
This question really does seem rather vague to me: Are you asking what shader complexity the engine can handle? (If so, then rdb has already answered for Panda’s side, I believe) What resolutions are supported? (… Unless we were talking about a specialist engine, such as Adventure Game Studio, I’d be surprised if both didn’t support all modern standard resolutions.) How many polygons they can push? (Isn’t this more bound by the graphics card than the engine in most halfway-decent engines?) Something else that I’m missing?
The above isn’t meant disingenuously: I’m really not sure of what you’re asking, not because I don’t know the answers (which I might well not), but because there are multiple ways to interpret your question, it seems to me, and I’m not sure of which one applies.
3) Critical Engine Features
Which features do you consider to be critical? Surely this varies from project to project? After all, a physics puzzle game might require a robust, deterministic physics engine, while a 3D rpg might require a good kinematic character controller.
4) Game engine speed
Answered for Panda’s side by rdb, I think.
5) General ease of implementation
This seems likely to depend heavily on how you prefer to develop, but I think that this question might have the most concrete answer of those that you’ve asked (from my perspective, at least):
I don’t know much about C4’s tools, but I will say that tools are perhaps one of Panda’s weak points. In particular, Panda lacks a good “scene editor” tool (such as Unity offers); I believe that a community-developed scene editor is under development, and at least partially usable, but I haven’t been following its progress and so don’t know its current status, I fear.
That said, Panda’s use of Python as a scripting language can make for some very smooth implementations. Look, for example, at this Panda “Hello World” program. It’s the first step of the manual’s tutorial program, and simply shows a Panda window, and calls for all of six lines (excluding spaces), I believe.
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I disagree: some questions really are vague.
Consider the question “what is the biggest building in the world?”.
What do we mean by “big”? Are we looking for the tallest? The one that covers the largest surface area? the one with the largest volume? Do basement levels count? And so on. Since the word “big” is poorly defined in this circumstance, the question is poorly defined.
One could, I suppose, answer all of the above, giving a detailed account taking the various interpretations and issues into account, but that’s asking a fair bit of the answerer, it seems to me, and the questioner may have simply wanted the tallest, and so get a highly superfluous response.