I like no longer having to track negative hp's.
I think the massive damage rule is silly. It may have some effect on low levels (level 1, maybe level 2) but beyond that if you take enough damage to die from massive damage then the math of the game has failed. It just does not make sense to me. I do like that further damage is an automatic failed death save.
One thing I have hated is the Spare the Dying spell (or whatever it has been previously called). I would much prefer that it stabilizes someone rather than bringing them up to 1hp. As a DM, if the PCs are facing a single foe (or very few foes) and the cleric keeps bringing an ally back into the fight at 1hp, then dropping the ally does nothing for me. I have no choice but to target the cleric to remove the allies getting back into the fight. I find this unsatisfying and I'm sure the cleric player would also. Now, if you were brought to 1hp and still had to track the death saves you failed, that would be fine, but since death saves get reset once you gain healing I continue to find this a frustrating event at my table.