I play Tiger's modern and mostly enjoy it. I'm not a specialist, but the main issues for me are:
1. Austrian Attack (white puts paws on d4,e4,f4).
2. Averbakh Variation (white puts pawns on c4,d4,e4).
I watched the recent DVD that Tiger made with GingerGM, and he says that the book recommendation against #1 isn't good. He recommends learning the Pirc instead.
#2 either leads to an early queen trade where you actually need pretty accurate defense (I got destroyed a couple times), or a super cramped position where white advances d4d5. I don't enjoy either, but it's probably because I haven't studied it enough.
@BlindFool , what has been your experience?