I am running through with a wood elf Moon Circle druid now. I am having lots of fun in the animal forms.

I tried using the method of casting a concentration spell then shifting to bear to fight, but druids by deign don't tank by avoiding hits but rather by soaking damage, so a hit or two in and the concentration was broken and the spell slot felt lost. If you want to try out the new cool control/ area denial spells (flaming sphere, spike growth, etc...) you probably want to go land druid.

I did notice there is no restriction against using metal armor, scale mail works fine, with a shield and club for shillelagh you can get really nice AC and to hit chance.

Used bird form to reach some rooftops I had never been on before and found some secret stashes, just some lore items, like books, so far but it has opened me to exploring more just for exploration's sake. Has anyone noticed we aren't supposed to get flying form at low levels under the 5e rules? I wonder if flying form will substitute for feather fall on the drop into the underdark.

The badger form is using the misty step code with shorter range. You have to see the destination, so going under walls and doors doesn't work, and the material you burrow through doesn't matter. For example the wooden tower at the top of the mountain, you can burrow from the ground at the top and exit through the floor of the platform on top without ever traveling through the empty air in between. I still feel like there are ways to abuse this I haven't found yet but I don't know how much I'll use it after level 4 and flying form. I did burrow to the bottom of a cliff by one of the bridges and it wouldn't let me burrow back up "too high" so watch out for one way trips.

Haven't tried out the cat yet.

Spell wise Spike growth is my new best friend. I have to assume they will make the AI smarter to keep out of it in the future, but for now whole packs of enemies will shred themselves just trying to get at me, I love it. the sphere is really cool too, I wish it shared initiative with the druid though so it felt more like using your action to move it instead of taking no action and then the sphere may get a turn later if you can keep the concentration up. Moonbeam is crazy powerful. I used it in the Blighted Village and from a rooftop, I could target a different goblin every turn and one shot them. I did always picture moving it though as the illuminated area moving along the ground and not just dropping another beam at the new location.