I do feel that for a moon druid specifically, it should be possible for wildshaping to be the defining feature of the class and they should be able to melee combat in wildshape and be effective. Which, in fairness, I think they they pretty much can in EA, as long as we don't expect a wildshaped druid to be as effective as a warrior class in melee, which would be overpowered considering their versatility.
As mentioned, the polar bear isn't bad for tanking at the lowest level, with high enough HP to soak up damage, the taunt ability to attract aggro from squishier allies, and the ability to cast Barkskin to increase AC.
Past level 3, the bear is less useful outside of specific cases where taunt or a meat shield are handy, but using the wolf form in conjunction with the weird house-ruled Flaming Sphere can make the druid a pretty useful damage dealer (with the Sphere basically being a tanky summon that can be brought into combat to attract aggro, do at least a little damage and provide a nearby ally to the wolf to trigger its pack tactics advantage).
I still found the wolf the most generally useful combat shape up to level 5, though the Deep Rothe could be handy in places with a lot of shoving potential, but by the end of EA their HP was lagging which meant going into melee was dangerous as there was a high risk of my druid suddenly becoming a squishy human in the midst of the fight, but I'd be okay with that as long as we get another decent form at level 6. The other forms I found more useful for utility (with the moon druid's Dire Raven being my favourite for scouting, though hopefully it'll be still better in the full release as I was told when I reported it as a bug that the issues it has with dealing with encumbrance would be fixed.)
My biggest problem with the moon druid was that I feel it should be able to rely on effective use of concentration spells to help buff, control or damage while in wildshape to help make up the power gap between its melee wildshapes and the melee effectiveness of warrior classes. But maintaining concentration in EA is unreasonably hard, partly because enemy AI focuses on breaking concentration though if a character is in melee I think that's fair enough, but also because it is just checked too frequently, potentially many times per turn, and I believe is also broken by some conditions that wouldn't break it in tabletop. Plus, there are a few concentration damage spells that moon druids should be able to rely on to help boost their damage output, like Heat Metal, Moonbeam and Chain Lightning, by casting before using wildshape but then still be able to use their per turn abilities once changed (which is per RAW), but the way Larian had implemented them in EA meant that the activation features were disabled in wildshape as though we were casting new spells.
