I think he's a decent rental to bring in for one of our own distant picks first round picks, but everyone is going to have to be realistic with expectations: Serge Ibaka is no longer a star.
1. Serge Ibaka is no longer actually good at defense. He is just barely a net positive by defensive +/- (0.7), and no longer protects the rim like he did in his prime (4.3% block rate).
2. Serge Ibaka does not single-handedly solve our rebounding woes. His defensive rebound rate is 19.4%, which is nothing special. (Yet somehow would still be #2 on the entire Celtics team because we're that bad at rebounding.)
If we are going to bring him in, we need to remember that he's not the super-elite 3-and-D guy he was three seasons ago. At this point he's just a slow power forward who shoots threes and plays average defense. That is still a valuable player, and it's definitely something we can use in the rotation, but he's not going to make us contenders.