Honestly, the only issue I have is that most of the fills are overplayed (where “overplayed” = “too loud and too busy”), which limits the number of fills I can actually use. I am usually able to find enough fills to build what I need, but I do find that I can, in practice, only use about a quarter of them.
One of the apparent issues that I have noticed is that a lot of the fills are designed as full-bar fills, and, in most circumstances, I only end up triggering the last half of them. This becomes a problem when the fill relies on the first two beats to set up the last two. For example, consider Blues Fill 18 that has a weird dropped kick to start the second half of the phrase.
Others are just plain weird. The “tribute to Phil Colins” opening to Blues Fill 14 doesn’t quite fit the rest of the song, and it is also a perfect example of the toms being too loud/overplayed. Blues Fill 16, because it essentially comes to a complete stop in the middle of the phrase, is of limited use outside of an outro. Blues Fill 41 and 46 similarly bring things to a rather abrupt momentary halt, especially when played at speed.
But there are some great fills that I always end up going back to, like Blues Fill 2 (build), 5, 6, 10, and 21. What these all have in common is that they all have strong, musical beats 3 & 4 – which is where most real fills live.
I don’t have time to go through all of the available fills at the moment, but that’s just sort of my initial response. And, to my ear, it really comes down to making sure the last two beats of each fill hang together on their own, and maybe easing up on the volume of the toms in the rolls.