I haven't actually given my actual opinions on the modpack so here goes. Keep in mind that i'm coming from the direwolf20 pack, so I will only talk about the mods that are new for me
Voxel Crap:
I don't really like the voxel stuff. Besides the menu and map i'm not really sure what else it even has, but there are like 5 mods. I will most likely disable them all when the official version gets released but I'm not sure. I actually like the new map a bit. I haven't noticed any major performance issues and it does what I want it to, so I'm not sure ifi'll switch to Rei's or not. Either way its just a bunch of client mods that can easily be removed/replaced
Gregtech:
I have very mixed feeling about gregtech. While I think its great that its included, and even turned on by default. I'm not sure that it should be on insanity by default. For me i'm up to the challenge but I don't think its great for new people, or people that just don't want some of the ridiculous recipes. As for gregtech, I do really like all the cool stuff it adds, especially the worlgen in the nether/end.
Minefactory:
I had switched from my own private modpack to direwolf20 and one of the biggest mods I missed was this one. I was very surprised, but very happy that they added it. It's probably a little bit OP but I deserve it because I have gregtech on insanity mode.
Power Converters:
Again, I was very surprised by this because of how controversial mods like this were in the community. I'm probably gonna use it a fair bit. I think the factorization converter is pretty useful because I don't want to set up a whole solar field for like two machines.
Flat Bedrock:
Its such a small mod and yet one of my new favorites. I absolutely love it
Nether Ores:
I don't really care that much either way about nether ores. I mean first of all I don't really go mining in the nether, especially when you constantly get attacked by pigmen and randomly blown up. But it is pretty cool to have when you are in the nether and see something useful. I do like having ore in the nether(like vanilla quartz in 1.5 or gregtech's) but when its unique to that dimension.
Petrogen:
I'm literally can think of no practical uses for this if you have power converters installed. I mean I guess it could save you a step but isn't it a crappy conversion rate?
Secret Rooms:
Very happy about this mod being included. I can think of so many ways to make my base really awesome now, especially using the gates and the ghost blocks. One of the mods I missed from my own modpack
Applied energistics:
Within a couple minutes of playing with it, it is definitely in my top 3 mods. My goal is to make a system that I can request any items in the game.
Advanced solars:
I used compact solars before and I don't really care much either way. I know advanced solars are supposed to be so much better but I don't really notice much difference. I actually like compact solars a little better by default because there are solar hats built in. But because gravisuite adds ultimate solar helmets I like advanced solars a little better.
Tubestuff:
Really awesome, I love the duplicators for testing stuff in creative, and the incinerator is gonna be really awesome for compact machines
Advanced Machines:
Its just a couple upgrades to some basic machines, I guess its useful but I don't really see the big deal either way.
So overall I definitely recommend switching because of minefactory, tubestuff, power converters, secret rooms, and gregtech. Applied energistics is most likely gonna be added to the direwolf20 pack either way.