I watched a couple episodes of a lets play for the Sprout pack and it certainly looks interesting. I really like the atmosphere of the pack. There are small animals like hedgehogs, bird sounds, swamps have croaking frogs, ect...
I might even download the pack and check it our in a single player game to see what it is like for myself.
EDIT: I installed it and was having fun with the pack and discovered a problem. The Sound System kept crashing on me. This is the background atmospheric sounds like crickets and other stuff. I logged out of my single player game but kept it open in the background to see if it is the internal server or the modpack itself running. It kept freezing for several seconds every minute or so. I then shut the client down and restarted it. I will let you know if this helped. I might have to turn off the atmospheric sounds to play.
EDIT 2 : Restarted the client and after a couple hours I start getting the lag spikes and messages about the sound system crashing. I do not know what is causing it. Hopefully it is something between the client and internal server.