Skills: Pre 3e you have percentile (Thief) skills, NWP slots or no skills at all. After 3e you have only trained/untrained. In 5e you have skills with granular proficiency, just like in 3e, except the math is flatter.
(Base) Attack bonuses: None in 4E, now they're back. Yes they're flatter but they ascend with level and vary by class (The fighter goes from +3 to +4 for example, while the cleric stays at +2).
Feats/Specialties: Non existent in early D&D, brought about in 3E their new incarnation vaguely recalls both 2E kits and Weapon Proficiencies from that same period and 3E feats more than their 4E counterparts.
Saves: vs Effect pre 3E, Defenses after 4E, rolling your stat vs a DC to save, relating to how you save against an effect is very 3E, except it has expanded to six saves. As such, the class bonus to a stat and the stat increases with level can be seen as advancing your saves as well.
Monsters: Monsters weren't really build "like PCs" in 3E either. You didn't go about building a dragon the way you would build a character. And the designers have already said this option will be available. Nothing is stopping you from building a NPC villain from PC bits.
Saying that the 5E Cleave is not like the 3.5 Cleave doesn't really constitute and argument about similarity. It's not the same game. Even the 3.5 Cleave is not the same as the 3E cleave is not the same as the Pathfinder Cleave. These are mechanical retoolings, nerfings, balancing issues.
But looking at the mechanical framework I would say 5E looks the most like 3E/2E, but with 4E's attention to balance, clean math and streamlining and some of 1E/Basic's aspirations to simplicity and basics.
Of course 5E is its own game. But I would say it's more like 2E/3E than both 1E or 4E in most of its systems by far.