Doesn't look any different really.
The difference isn't only how he's being marked and how teams defend, it's also the complete lack of a good system that the players can feel comfortable with, where they play as a unit and read eachother well. Right now everyone look lost, and Messi gets the responsibility of basically beating two lines of defence himself, and at times he still manages to do it. His insane passes, often after a quick dribleraid, also open up defences like a corkopener very often. It's just that the movement, linkup and general chemistry in the final third is nowhere to be found, it's just slow and has a feeling of always being too little too late - and Messi pays for it more than anyone.
He is either marked by 3 players in his back if he plays further up the pitch, sometimes making it impossible to even pass the ball to him as he can't even receive it without being fouled, and when he plays deeper and initiates something, it all stops when it comes infront of goal anyways, because the link-up play is dreadful. The result is frustration and lots of crosses. I have for instance never before seen him try this many headers for Barcelona. You know something is completely wrong tactically when we have a 1,69cm tall targetman...
Of course he's not in the form of his life right now, but that's besides the point. Last season was also sometimes too slow and low-pressing tactically, but at least we had a complete system with an identity that the players were comfortable with and that they intuitively understood - simply put, it played to their strengths. There was way more movement in the final third, and the players combined together with some nice passes in the buildup and collectively broke defences down.
It's not like La Liga teams suddenly drank a strengthpotion or cracked some supersecret code on how to beat Barca. We're just playing really, really shitty right now. In fact worse than in many, many years. The tactics/system or whatever you want to call it simply doesn't work at all, our players just look completely lost and out of sync. The motivation is there, that much was obvious today, I think all of them fought hard.
Luis Enrique can't come to Barca quickly enough...