The only reason anyone ever really liked Ice Hunter was because Oda designed some characters. The arc itself was ridiculously bad. Rainbow Mist was chock full of dorks in clunky looking battle suits, crying kids, and an old man who can flick bottle caps. Nice try, but fail. The goat arc isn't worth mentioning. Neither is the Millenium Dragons/Apis arc…but I will. It's chock full of...nothing interesting. It does explain the weird guy they decided to spoil the canon for no good reason with while they were going over the reverse mountain.
G8 was indistinguishable from a typical shorter arc, so that made it worthwhile, even pretty good. I liked the individual episodes, Zoro's with Giant Whale Dick/Johnny and Yosaku, the Robin/Chopper one, the Usopp firecracker one, even the Sanji one (as I enjoy the cooking and the stuff) after Arabasta and the one during W7. The Brook one just made Brook look way more pathetic than he is. Generally, the individual character building ones are worthwhile. The ones based off the cover stories are decent, and I didn't mind the Edo-era ones just because it wasn't like watching a parody of One Piece instead of the real thing...just something different with the same people.
When I watch most of the fillers, it's like I'm watching another show that is making fun of One Piece. Which isn't bad some times, and it's pretty fairly typical of fillers with most of the big ongoing series (Bleach, Naruto, etc). But I really don't enjoy them unless I'm slightly inebriated. I found Ice Hunter almost unwatchable, but I have to admit, the fillers are getting better. At least they're not just all focused on the stupid characters that the filler writers create, and make the Strawhats take a backseat to the plot.