My experiences in a DL campaign after 7 levels...
FIGHTERS!
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1. I no longer envy the fighter's damage dealing capability. The fighter is still a fighter. A very limited, specialized class that does damage. It's about all he does.
The Protection-style fighter has saved folk's hide more than once IMC, and is solid at dealing damage, with a sky-high AC. He tends to have bad luck (he's hit a LOT more often than he should be!), but he's got staying power and a lot of party enhancement.
In a low magic game like 5th edition, it's tough to be a fighter. No easy access to flight, protection from elements, movement enhancing powers, and the like. Totally reliant on casters that are highly limited. If they are not archery specialized, they suffer immensely against highly mobile creatures with reach and powerful attacks like breath weapons.
IMXP, this has not been a major problem - mobility hasn't gotten ANY monster out of reach of our melee machines, and while they're hit pretty hard by monsters that hit with area effects, their survivability has neutralized those effects on the rest of the party.
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CONCENTRATION!
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It's tough to be a caster. This concentration rule is highly limiting. It's very hard to buff people due to concentration. You are very limited in spell selection once you have a concentration spell up. No more casting protection from energy with fly and invisibility. You can cast fly. Then spend your time making sure you keep it up, so the martials have a chance to engage the flying dragon with reach.
IMXP, Concentration hasn't been that awful. This may be in part because we're a party that does not really buff (I know
invisisbility, the other party caster knows
fly, mostly we use those spells on ourselves). I employ a lot of Concentration-oriented debuffs though, and I haven't found it that limiting - I can't polymorph and hypnotic pattern someone, but
either of those prevents enemies from doing much, so I don't need to do both at the same time. And I can't do either one when I'm invisible, but that's entirely fine - invisible isn't for fighting.
You really have to coordinate with other casters due to concentration.
...
you have to worry about spreading out to avoid the breath weapon or AoE attacks.
These are positive in my mind - it's about time people stop relying on Waggly Fingers Magoo to to their thinking for them.
The lack of access to consumable items along with limited spell slots and the concentration mechanic leads to logistical nightmares if the DM has intelligent monsters wait until spells and spell slots expire.
I dunno about lack of access - I've got all the healing potions and alchemists' fire
I need. And again, our experiences may differ because my party doesn't have a lot of buffs: it's not usually critically important that
fly or
invisible be up in a fight.
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DRAGONS!
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It is nearly impossible to defeat an intelligently played dragon in 5E.
I killed two simultaneously last session with a
sleep spell. I mean, they were like, babies, but still.
If they fly around using lair actions waiting out spell durations and spell slot depletion as an intelligent dragon would do, you have no shot at beating them. They have an unlimited breath weapon that can keep recharging. You have no means of limiting the damage to an entire group and extremely limited means of mitigating the damage against even on member of your party. You are meat for their larders.
I think the fights my group has had with dragons are a little skewed thanks to some story-based Dragonlance shenanigans - we're fighting them on the march, two out of the three dragonfights has been with allied dragons, and our party has two dragonlances that are basically dragon-slaying machines. Two out of the three have also been with
multiple dragons.
...all I know is that my gnome wild sorcerer absolutely adores causing these things to plummet out of the sky by disabling them.

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HEALERS!
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4. You need a healer. There's not getting around it. You need combat healing. Things hit hard. The damage adds up. An inability to heal in combat leads to major problems, especially when you get hit by hard AoE damage. Rough game that requires a good healer. You almost need a cleric or Lore Bard built for healing.
Healing potions + fast combat have IMXP worked against this idea - if someone goes down (as our paladin often does), the fight's over in time to stabilize them and spend some HD. Healing potions get folks back in the game if they drop early. Our party has not had a cleric, and has little to no in-combat healing (a ranger who RP's it so she usually doesn't cure us during fights, and a paladin who would prefer to smite). We've been chuggin' along just fine.
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PALADINS!
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5. Paladin is the best martial. A paladin's ability to defend himself and unleash burst damage comes in immensely handy when fighting things like dragons. Being able to unleash burst damage when the dragon gives you an opportunity to hit it is immensely helpful. Having better saves and the best self-heal ability is immensely helpful given all the different saves for main special attacks, legendary action attacks, and lair action attacks is extremely useful. Having immunity to the frightened condition is immensely helpful. The paladin is an amazing martial class with a high level of useful versatility.
Eh.....the one in our party is known for dropping pretty quick, and smiting pretty hard. He holds his own along with our Fighter.
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ROGUES!
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Rogues are nearly useless against creatures like dragons or with truesight or blindsight. Completely eliminates their powerful stealth abilities. A paladin doesn't need stealth to use their most powerful abilities.
Our party rogue is a multiclassed battlemaster, so she doesn't rely on
hiding to get advantage. In fact, with all the disability I'm tossing around, even if she didn't get it from superiority dice, she'd probably get it half the time without hiding anyway.
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BARDS!
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6. Bard is pretty amazing as well. Bardic inspiration and Cutting Words can be lifesavers. Their mix of offense and defense can be helpful. A lucky crit by the bard with a chromatic orb won the day. Our two martials and cleric were dead. My wizard had dropped from a lair action attack. The bard hucked that orb and rolled 20. It did the job. Though it wouldn't have been wounded enough if not for the paladin unleashing a bunch of smite damage on it. The fighter did a total of 12 points with an arrow. He was chewed up by the lair actions and breath weapon before could do much as was the cleric. Concentration made defensive casting impossible for the group. No way to buff everyone against the breath weapon damage.
I dunno, my bard died at 4th level because he tried to be a hero, and focused on buffs, so I didn't get a good comparison, but I'm enjoying my wild sorcerer probably just as much.
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LEGENDARIES!
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7. 5E legendary monsters are rough. If you play them intelligently, can really make life nightmarish for a group. They usually have a nice combination of offensive and defensive powers that create real problems for a party. If they go all offense, they can be easy to kill. If a DM uses their offensive and defensive capabilities to the fullest, the fights are rough. We haven't had a party decimated like this in ages. This was against a standard module designed encounter we're used to crushing. The dynamics of caster power have changed dramatically. Casters can't mitigate damage like they used to and they have to be very selective with their spells with the concentration mechanic. Healing is far less powerful than it used to be as well, though just as necessary as previous editions. All these factors making 5E very rough in combat.
The one time annoying legendary stuff came up was when a dragon auto-saved after I tried to drop it from the sky. *SIGH*
Being legendary didn't help that beholder I polymorphed, though.

THAT thing dropped like a rock once I turned it into a bee. It might've been scary, but
my gnome is scarier.
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Overall, my experiences are quite a bit different!