It's big enough that you can have pretty different experiences in different kinds of articles. I mostly write history stuff, and my experiences there are pretty good. People seem to appreciate new articles on stuff like a Greek archaeological site, a 19th-century politician, etc., or expansions to existing articles, as long as the information has references. [Actually that's my own theory for part of the decline: around 2007 it became much more necessary to include citations for your additions, which raises the barrier to entry.]

In history articles, things mostly get contentious around subjects that seem inherently contentious for non-Wikipedia-related reasons. The archives of the talk page for "Armenian Genocide" are rather extensive and not always cordial, because people have very different ideas about what should go in it, some of them strongly held. But it's at least converged on a decent article imo.

When there aren't the same passions around the historical disputes, I've found the environment pretty supportive. I worked on a biography of an ancient Roman politician where there was quite a bit of inconsistency between what different classicists had written about him, but the discussion was just trying to figure out how we should deal with that in the article, and where the mainstream historical consensus lay (if anywhere), not hugely partisan or anything.