Honestly one of the best games I have ever played! I have read a lot of one star reviews and I will go over them here.
I have seen a lot of complaints about getting banned, from my view I think the banning rules are perfect. If you say something mean or disrespectful in the chat you get banned. People were complaining about how they said that some nasty thing in the chat and they got banned. I mean this game is made up mostly of kids and some are very young. Saying curse words in the chat should result in a ban, thankfully we do not see many people typing in chat anyways though.
Another thing I see in negative reviews is complaints about items. Now with the new drops that came out you can just play and get great items! Yes if you want a really good looking item or decal you have to pay for it but I mean they gotta make money somehow. And if your smart you can find a way to get good items just from trading.
More complaints are about the toxic community. I can definitely relate to this and I do agree that the community can at times be very toxic. I personally can usually just ignore it or report them if its really bad. But a lot of people just turn chat off or have only team chat on so you can just say important stuff to your teammates.
I have also seen complaints about the lag. People say they have the best internet the world has to offer and stuff. And yes the game does have lag problems but I have not experienced any in over a month. You might have good internet but something has got to be messed up with it or your in a area that sometimes doesn't get the best connection. People also complain that games like fortnight or whatever don't have that lag, well Rocket league is a physics based game where shooter games not so much. In a shooter game you can shoot someone on your screen and maybe you were lagging, so the game makes it look like you narrowly missed. But Rocket League can't be made in a way where if you shoot the ball at the goal and it looks to everyone else that it went in but to you that it did not they cannot make it just not be a goal for you because you lagged.
Also a lot of people say that the matchmaking is broken... What? I simply do not understand what is broken about it, they say that they are put with people that are way better or worse than them. If you are playing casual mode yes this will happen a lot. Casual is not nearly as strict with the MMR as competitive is. In competitive I have never played with someone that is way better or worse than me unless people are in a party which is very very very rarely and they would only be worse for you.
Another thing is people get mad for getting on the same team with players that are "trash" first off psyonix cannot control who you get paired with. Second if you are playing ranked and you get put with a bad teammate you are just as bad as them if you have the same rank. And they probably are thinking that you suck.
Almost all the negative comments are from toxic players that get mad because they had a bad teamate, have to pay money to get a really expensive item, the ones that cannot rank up and lag excuses. The only one star comments I understand are the ones talking about the toxic community and I think its the only problem with rocket league. But really I don't think that there is one game that does not have some sort of toxic community and like I said you can just turn chat off.