People can react wildly differently to relatively innocuous presentation decisions like this, oddly enough. I've seen people wanting to toss an entire resume simply because the candidate had "the gall" to list a hobby project under the "Experience" header.

My personal preference would be to simply list everything in one section and classify each thing that is a hobby/indie/whatever project as such rather than split them out. But that's me. So I'd say by way of advice that you should make the decision based on how the results look. If splitting them would leave an unbalanced "non-professional experience" section with way fewer items, for example, I don't feel like it benefits you in any way. If you have a relatively even split, sure. It's probably not a decision that is worth worrying about too much, as long as you aren't trying pass off hobby work as professional, somebody-paid-you-for-this work you'll probably be fine, but you're always going to run the risk of people with their own weird personal views on how a resume "must be" structured.

Both, there's no such thing as bad-experience.

All kind of experience is good.

I'd prefer someone who worked on 20 volunteered projects rather than having a guy who worked for 5 years on the same "professional" project.

Variety makes a difference.

Like above, it all depends on the interviewer and it is something you cannot predict.

Personally I have a slight preference toward keeping them apart.

For somebody experienced in the workforce I expect to see headings basically like this:

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Major Game Titles (Move to the top of the pile of applicants)

Work Experience Details (Wow me with details)

Education, optionally hobbies etc. (Tell me you have a broader background)

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For recent graduates just entering the work force I expect to see headings basically like this

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Education (This is your biggest set of accomplishments)

Work Experience (Show me you can hold a job flipping burgers, sweeping floors, or writing student code)

Hobby Game Projects / Portfolio (Show me you care about games)

(NO skills section, show don't tell.)

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For a recent graduate with a serious portfolio of games, I don't mind the order swapped a little:

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Hobby Game Projects (Your finished games are awesome, they are most significant)

Education (School is second most signicant)

Work Experience (You can hold a job flipping burgers or writing junior level code)

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If you want to mix them up, keep them all intermixed, I can cope with that by putting on my resume-reading glasses. When I'm in resume-reading mode I assume everything is inflated, that things like "Owner" and "CTO" mean "My buddy and I started a hobby project that failed", that Senior Developer with anything less than eight years work experience means "Worked at a desperate company giving out job titles and stroking egos rather than treating employees fairly".