I haven't played a lot of IA4 to give very specific opinion, but after trying it out a bit it's giving me feel a bit confused overall.
About the positive stuff:
-I really love the idea of backpack/vehicle locking, it's fixing one of the problems that's been following IA for a while, which is people messing with your stuff without your permission. I believe most of us in the past experienced some pointless and annoying arguing with people related to that situation, which sometimes even ended with giving up on playing more that day. (I love arma and games overall for giving us possibility to escape from every-day troubles, and I don't feel like having to deal with more of them virtually.)
-New revive system. Feels much better than the previous one and I think it's less buggy when it comes to reviving (I don't recall any situation where I wasn't able to revive someone. In the old revive system problem with reviving is more like everyday situation.) After being shot down you don't end up thinking "Not again..." and can actually hope to get help from someone and enjoy another chance instead of respawning over and over due to lack of medics around or having to deal with 'revive bug' yourself. The only thing you can miss from old revive system is being able to carry/drag someone. In some situations really helpful or even necessary. Still hoping to get it back one day. (#BlameStan)
-Possibility to play other faction than NATO (it brought the feeling of something new to enjoy/use).
For me the new Reward system is the only thing giving me mixed feelings. As @Xwatt mentioned, it has a lot of potential to fix the problem with side mission rewards and people fighting over them. I also think the system should include only vehicles, without any additional gear to purchase (about that below).
Now the negatives:
-Limited arsenal. Unlimited arsenal (kind of unlimited) is one of the main things you love IA for. It gives you the ability to approach the ongoing mission however you want, in your own style. You can easily change your style wherever you get bored of it or when you need to. There's a lot to choose from. That's why I don't like the idea of including any gear in the reward system, feels like they just took away some freedom from you. The only place where gear limitation fits and works well from my perspective are zeus missions. For IA it can get quite monotonous.
-Groups and roles is the thing that confuses me most. Every time I look at the groups panel it feels so illegible, and I just end up reading whole group panel few times in a row just to figure out which role is free to take. Maybe that's just the lack of colors and specific style to make it a bit more readable, but I guess that could be changed.
-More points for being in the area of operations. It feels like it would reward players for choosing more aggresive playstyle, which can lead to a bit of greedyness when it comes to points. I just imagined how it would work for friendly armor. Once you spend some time in the armored squads, you realise quite fast how easily it is to lose any vehicle if you get too close, AI is unforgivable once they spot you (especially now when the AI became more challenging). Whenever you think differently on another day and another approach, they quickly remind you how wrong you were this time, again. Sitting a bit away from the mission area is a common thing to anyone who tries to make some good use of the vehicle as they try to support friendly infantry. Being greedy for points can push many people too far and and they will just end up losing helpful assets. Also, freedom when it comes to playstyle feels a bit like a tradition, something that shouldn't be changed.
I would love to see a good mix between old IA3 and positive aspects of IA4. That could be something to make public server even more enjoyable, bringing a bit of freshness without unnecesary changes to something that works just well. I believe I could get used to the IA4 the way it is now if I had to, but the question is, do I want to? At the moment - not really. That's not something I would get back into every day with some excitement.