Well, some Fluff changes isnt that bad.
Look at Squigs:
Orks boarded A tyranid ship and found squiggly beasts, they freed the squiggly beasts and brought them back with them.
Squigs are part of the Ork race, before orks spawn, squigs will spawn in enough number to create a food supply. there is a wide range of squigs, ranging from diminutive hair squigs, to Squiggoths.
Squigs are the Ork's source of Food, Fuel, Music, and Entertainment. As the Elusive Brown surprise squig remains the most exciting part of going to the Drops!
The fluff that I tend to see as "bad" is the power creep effecting fluff. I mean... in another 6 editions(if the game lasts that long!), There will probably be a point where a Ork Warboss Headbutts a marine so hard the planet under their feet shatters.
"The Humans say, If you build it they will come. Alas each time I build something, Most people tend to Run." -Musing of the Dreadboss.