My favorite thing hands down is bounded accuracy. Nothing else even comes close. I'm so grateful to be rid of the arms race I can't even tell you.
Right now my least favorite thing, and I'm not even sure it is real, is a lack of variety. From the dungeon master's screen, it feels like we're back to the AD&D2 paradigm of "I attack, you attack, the monster attacks, the mage casts a spell, I attack, you attack." I feel like we may have sacked some of the breadth of D&D along with the unnecessary amplitude. My players don't seem bothered, though.
My feeling is that variety will come down to the ability of the DM. I love that. If you want to do something creative, the DM must come up with a ruling on the fly. He has a simple mechanic to work with to do it. All the old things are possible, but the DM and player have to discuss it an work it out.
Scouting and movement are fluid now. I haven't had so much fun scouting ahead and taking out sentries in ages. Passive Perception against Rogue Stealth is good fun. Sneak up, hit them with sneak attack, and move. You can move back and forth from cover easily. Help action is simple and gives a powerful advantage at useful times. I think the variety is still there. It's going to take some time for players to get used to how it all works. And DMs are going to have be more open to player creativity. If a player wants to disarm an opponent, the DM is going to have to come up with the mechanic on the fly. If the player wants to knock a guy off the edge of a cliff, he's going to have to decide the mechanic on the fly according to things like distance from the edge, relative size, strength, and the like.
It puts so much creativity and DM/player interaction back into the game. That is where the variety will come from like it did in the old days. No more slogging through a ton of rules. Instead the player asks if he can do something, describes how he wants to do it, and the DM thinks out how it would work and decides how difficult it is. I love that about 5E.
As far as the initiative order, players did that anyway. 3E was move, attack. Move, cast spell.
Now with 5E, you can move, attack, move, attack, bonus action disengage, move to cover. It's so much more fluid, imaginative, and fun in my opinion. Until people get older mechanics out of their head and understand the new fluidity of combat, it will seem less varied when it is actually more varied.