I miss him occasionally, but I do not want him to return to the band. He was too much of a control freak (mistakenly referred by him as OCD, which is a true disorder and something super nasty) and his last years in DT were basically him driving the whole thing and taking the shots on everything. Things might've ended up differently for him if he wasn't so obsessed with him being in control of everything (bootlegs, setlists, press, tours, etc.). And, as many might agree, his "hey, my voice has balls, let me sing along with James so our music can have more balls" approach wasn't the best thing that happened to DT.
Also, his drumming became stale in the last records. I was listening to SDOIT the other day and was in awe, the drumming sounds so fresh, so inspired and so creative in that record that it's ridiculous. His live playing began to suffer, and this I began to realize until my "OMG MP BEST DRUMMER EVER DRUM GOD" phase faded away. I used to defend him (and everyone else in the band) so blindly that it was ridiculous
He is a great drummer, but his lack of practice (he has said he doesn't practice anymore) began shaping in sloppy performances. I remember seeing A Nightmare to Remember live, and it was...you know, sloppy. The thing IMO that always made Portnoy shine was his drive on stage and his creativity into composing drum parts. I understand why he is such a big influence for young drummers nowadays, but truth is that he's no longer in the top tier of drummers like he was back in the 90s.
That being said, his Ytse Jam bootlegs thing and his communication with fans is something I do miss. A lot. But hey, give and take.