His playing is too predictable. for example in the song Paschandale, he repeats the same beginning in each of his phrase (approx 1 measure) a bend, a quick release bend and going lower with short notes, roaming there a bit, higher, then repeat the loop.
But!!! he has many great moments, like the solos of From Here To Eternity (beginning of his part, tremolo bar, which goes perfectly), DOD solo (especially tapping part) and the intro of Lord of The Flies. He makes some very good fills in concerts too. (So many moments I can't count)
What I really like in Janick is his songwriting. He writes most interesting Iron Maiden stuff since Fear Of The Dark. He wrote most progressive songs like Ghost of The Navigator. Intro to Out of Silent Planet is his signature on it. It's always good to have a distinct style both in playing and songwriting.
Lastly, I only wished his songs weren't touched or influenced that much by Stevie, as in the case of Dream Of Mirrors. a beautiful song, but becomes unnecessarily long and repetitive, by repeating whole intro-verse-chorus part a second time and at the end of song. like most of post-Fear of The Dark Harris signature tracks...