For the last 9 months or so I've been running a 5E campaign using the Tomb of Annihilation.
I cannot emphasize enough how much I hate the 5E WotC adventure format:
First , referencing monsters instead of inline stat blocks sucks. It is up to you to look them up from disparate sources. So you'll need several books open while running, or to pre-compile the information.
Second , the adventures are overloaded with words. Try scanning these adventures as you are running; the adventure scatters information throughout in a baroque economy of words.
Third , they try to play zone appeasement. Is Tomb of Annihilation of hex crawl? If so, the map is shit and the area is mostly empty–except for the random encounters that at best add flavor. Is it a site-based adventure? Is it a time-based adventure? The scale of the map ensures any intertwining stories are lost. Why am I wasting 45 minutes on a random combat encounter in which there will be only one between long rests?
What I like, however, is that 5E is a great player facing game. Player characters have lots of options - there are plenty of bells and whistles with which they can engage into a robust-enough rules system.
The math is almost to my liking; Though truth be told I like clever solutions never require rolls and phoned-in solutions are more likely to fail than succeed (e.g. “I check for traps, roll dice” or “I bluff the guard, roll dice”).
I like that save or die (or incapacitated) effects are mostly nerfed. The original design principle and assumption that by the time a character is rolling a saving throw, they've already bungled something. However, with 5E, there is an assumption you'll be charging into threats; After all XP is now combat based instead of gold piece based.
Two sessions ago, the characters began the session under attack from assassin vines. They rolled initiative and as part of the count, some skeletons rounded a far away corner (along with some veterans and a mage). The resulting combat was intense and near deadly. After 7 rounds of combat, they dug it out, and scraped away a partial victory; The assassin vines were dead, a veteran and the mage had fled. This combat took 2 hours, and I believe most everyone enjoyed the ebb and flow.
Last session, they tracked down the mage, laid an ambush, and got the jump on him…with surprise. The combat was over in less than 5 minutes.
The big combat was great and felt very “modern” D&D. The ambush was great and felt very OSR; They planned, they pushed themselves, and the reward was capturing someone without an expenditure of resources.
Ultimately, I want more of the second. Reward clever play. Of which, WotC adventures appear to instead introduce set pieces that focus on multi-round combats and execution of character builds.
Which begs the question, in a role-playing game, am I engaging as my character? Or am I telling my character what actions to take?
From a GM stand-point, I much preferred the ambush. The characters had an agenda, laid out a plan, and executed that plan. From this they gained information to further take meaningful action. The combat was decisive and quick, and it resulted in a substantive fictional state change.
We're about half-way through Tomb of Annihilation and I'd love to wrap things up. Soon we'll move from hex crawl into dungeon delve. I'm already longing for quick decisive combats.