I'm mostly a RPG player.I'm primarily an MMO player. Here's how I see 4E moved closer to MMOs (at least those of the WoW generation)
1, More defined roles.
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2. The encounter as the central unit.
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3. Powers for all classes, especially non-magic ones. Before 4E, warriors just attacked. In 4E they used specific powers.
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4. More emphasis on tactical movement, including positioning and things like knockbacks, etc.
As I think I already mentioned upthread, the idea of "roles" - front-line fighter, skirmisher, wall-caster, etc - was something I was already fairly familiar with from RPGing (Rolemaster emhasised it more than AD&D, except for the buffer/healer which is a straight-down-the-line cleric).
The idea of "powers" rather than basic attacks was also something I was familiar with from Rolemaster. And it was present in 3E, too, via feats. Not to mention different forms of implementation in non-D&D RPGs like eg The Dying Earth. The innovation in 4e, from my perspective, was not giving fighters powers, but recognising that rationing schemes that had been part of the game since 1974 could be extended beyond spell casters to solve the problem of giving players of martial PCs interesting options while avoiding either low success chances or spamming. The insight here is that rationing of powers can be on a metagame logic rather than an ingame (Vancian) logic. This design insight is something I associate with indie-RPGs (though "plot points" existed in games like James Bond going back to the mid-80s), not MMOs.
The encounter as the central unit of play was a feature of indie RPGs since at least Maelstrom Storyteling in 1996. I discovered it, by accident and evolution of my GMing style, in the mid-80s, but became more consicous of it since reading the Forge in 2004.
For me, the only new feature of 4e was the tactical movement/positioning, although there were earlier RPGs that made positioning a central element of melee combat (eg Burning Wheel).
I think if someone was familiar with developments in RPGs since the mid-90s (especially outside D&D/d20) then 4e would be less surprising. To me, it basically read as the version of D&D you would write if you had read the Forge essays, the Foreword to Moldvay Basic, and like fiddly mechanical options in combat (and so had a history of playing Rolemaster, Runequest or a similar rules-heavy game).