This is still one of the best, if not the best Call of Duty of all time. But unfortunately this isn't enjoyable to play anymore (at least in 2018+) - By the time I realized that VAC isn't that good at filtering out unfair players (at least in MW3). Almost every 4th match I have run over a cheater, modder or whatever you wanna call them. I got the feelings that VAC isn't even active anymore for this game... byside the fact I see no reason why Valve should turn VAC offline. I've also heared that it's Activision themselves who still ban cheaters (at least when they perform too obvious).
So for me personally, it isn't enjoyable anymore which DOESN'T mean it's unplayable. You can still get some rounds with no cheaters ofc. where you can have your fun.
All in all I have to say that it's not worth to buy anymore. The gameplay-quality isn't the same as it was - which also means it isn't worth 20 Euros!