The only depression you named was 1929. 2000 was barely a recession. 2008 was more severe but...still not really. The US unemployment rate hit 10% which is high...but most countries Europe have had rates at this level for decades. For reference, the current rate in France has an 8 handle.
In terms of depression vs recession, to put it simply, the risk is that we move into a situation from which escape is difficult. For example, and this is a hypothetical, everyone in airlines loses their jobs, this causes demand to fall, more people lose their job, supply falls, etc. Depressions destroy resources. Recessions reallocate resources.
So I don't think this looks particularly serious...if policymakers act promptly. This means ensuring that credit is supplied to companies that are solvent and firms that insolvent are shut down. The only thing that looked bad going into this was everything going on in tech, and the level of corporate debt (and its distribution). There is still a huge amount of complacency here (a big part of this cycle has been ETFs...I talked to a quant the other week who is neck deep in corp bond indexes who confidently told me defaults wouldn't rise...the guy has never looked at a balance sheet in his life).
But one very bad sign is gold and govt bonds falling with equities. This is probably being caused by someone running a risk parity strategy trying to get out of their positions but it could also be a sign that liquidity is disappearing (and people are selling whatever they can sell). Equally, last week the momentum tech stocks weren't really selling off, and now they are really starting to tank (although this is probably a good sign long-term, short-term people are clearly panicking).
Also, as a point of history, there was no "mass defaults" in 2008. The default rate definitely rose substantially and there was a liquidity crisis but this ended up working itself out and the vast majority of these assets came good (we know because the govt bought them all).