I'd say there's more review on m.o projects than at any medium-large company I've worked at. It's not hostile at all, and I've learned something the times I've cared enough to shepherd a patch through that process.

I don't think it's unfriendly to newbies at all, other than the size of the codebase being so large that it takes considerable time/effort to understand well enough to make a patch you're willing to work through getting integrated.