I know that Magic Resistance like the Yuan-Ti have used to be considered borderline OP the way monster statblocks used to be configured. However, with the shift towards monster abilities replacing many spells on statblocks, is it still really that powerful? I’m curious what the community thinks about this.

Well, it said "and other magical effects" in the Volo's version. The Mordy's version cut that part out. When you put that together with the monster 'spell-like abilities' in Mordy's, I would say that it's a lot less powerful, yes.

Edit: It's still good though. It's not active enough or flashy enough to drive my choice of race on its own, but it's decidedly stronger than some of the features that would.

Maybe this is a cop out to say, but it seems pretty campaign dependent. I just finished a campaign with an ancients paladin, and the spell resistance hardly came up. There were just very few casters. When it did, it was clutch, but mostly it didn’t get used. 
It’s the kind of thing that can be super-powerful, or it can be practically a ribbon ability.

Quote from Xalthu >>

Maybe this is a cop out to say, but it seems pretty campaign dependent. I just finished a campaign with an ancients paladin, and the spell resistance hardly came up. There were just very few casters. When it did, it was clutch, but mostly it didn’t get used. 
It’s the kind of thing that can be super-powerful, or it can be practically a ribbon ability.

 I guess I mildly disagree. I also played an Ancients Paladin in a campaign from I think 4th to 20th, and the Aura of Warding kicked butt in that campaign (Dungeon of the Mad Mage). Yes, sometimes you'll go whole sessions without using it against an enemy -- but, it allows your allies to recklessly slam AoE spells right on top of you, which is pretty neat for a front-line character like a Paladin. I think, if it weren't for that, I'd agree with you that it's unreliable, but the added utility of making friendly fire safer pushes it over the edge into just being good.

Quote from ChoirOfFire >>

Quote from Xalthu >>

Maybe this is a cop out to say, but it seems pretty campaign dependent. I just finished a campaign with an ancients paladin, and the spell resistance hardly came up. There were just very few casters. When it did, it was clutch, but mostly it didn’t get used. 
It’s the kind of thing that can be super-powerful, or it can be practically a ribbon ability.

 I guess I mildly disagree. I also played an Ancients Paladin in a campaign from I think 4th to 20th, and the Aura of Warding kicked butt in that campaign (Dungeon of the Mad Mage). Yes, sometimes you'll go whole sessions without using it against an enemy -- but, it allows your allies to recklessly slam AoE spells right on top of you, which is pretty neat for a front-line character like a Paladin. I think, if it weren't for that, I'd agree with you that it's unreliable, but the added utility of making friendly fire safer pushes it over the edge into just being good.

 That’s kind of what I was saying. It’s campaign dependent. In yours it was great and useful, in mine it didn’t come up much at all. In mine, the party had no one with AoEs, closest we had was an alchemist artificer, and the enemies weren’t really casting much at all. It wasn’t even intentionally low-magic, it just worked out that way. 

Yes it is somewhat campaign dependant with lower magic campaigns it’s utility is less but anything that blocks/reduces magic is always going to be significant and powerful in D&D.

Thanks, I appreciate the insight all.

Given that the stat block for freaking Vecna that was released last year only has three spells that the nerfed version of Magic Resistance applies to, I'd say that it's definitely not an OP ability anymore (if it ever was).

What was OP for resistance was the original Drow resistance back in 2e - something like 90% resistance. Drow, ropers and mindflayers all had 60%+ resistance to spells and spell like effects - that was nasty!