It doesnt surprise me that he's split fan opinion, he's got attributes that many people look for in a good old fashioned anchor man but lacks ability in many areas of his game. I don't think he's shockingly bad, but I also don't think we would be mad to get rid. Like people said above, he's good at pressing, full of energy, not bad at tackling.
But also, as people have said above, lacks strength, dreadful on the ball, no footballing intelligence whatsoever.
People saying he needs to be surrounded by better players doesn't work for me. This is modern football, every position on the pitch is being optimised in terms of player ability and performance. Ball playing centre backs, ball playing goalkeepers, creative full backs, goalscoring wingers.
Douglas Luiz is a far more intelligent defender, makes clever fouls and interceptions because he can predict the next 5, 10, 30 seconds of play. But Dougy also offers something going forward. Excellent range of passing, a goal threat, intelligence on the ball.
Nakamba will never be good enough to replace Douglas in the team and there isnt room for two of them in a 4-3-3. If Douglas was injured and replaced by Nakamba, the drop in footballing quality in the side would be damaging and the rest of the side would have to work so much harder when in possession.
In my opinion, Nakamba has a place in the squad next season for the exact role he was used for in the final few games. Bring him on to play beside Douglas when we are ahead in a game and the opposition are dominating possession. Or start him in a 4-2-3-1 beside Douglas in games where the opposition have a far stronger midfield such as City and United.
In time, I think he will need to be replaced with a player closer to the abilities of Douglas Luiz, Fernandinho, Fabinho, Rice etc.