As a tinkerer and designer (and now paid writer, go me!) I'll list off the things I like best about Level Up.
1) Class redesigns centered around the classes feeling distinctly different.
Yeah, an O5e Barbarian is different than an O5e Fighter, but most of the differences are hard to see in play. They both move near an enemy and hit it as many times as they can. And until at least the back-half of leveling: That's the same number of times!
But now? Fighters are built around having a ton of interesting combat maneuvers. Berserkers slam down crit after devastating crit. And while the Berserker -does- get some options for combat maneuvers, they're both limited in number and styles, which creates a wider variety of potential differences between a given fighter and berserker.
Similarly, Warlocks are now Spell Point Casters which helps to further differentiate them from Sorcerers and Wizards. Add in the floating casting attribute and now you've got an even -more- flexible and wild design that plays into different ways to gain occult powers. Worshipping powerful occult entities? Wisdom. Making a deal? Charisma. Apprentice Wizard reads the wrong book? Intelligence.
Add in the actual narrative benefits for Social and Exploration encounters of each class and they get even more wildly disparate in theme. I often wind up thinking of Druids as just "Nature Clerics" but A5e makes Clerics into Proselytizers for their religion which I both hate and also really like.
And because these classes are doing their thing in unique, or at least significantly different, ways I get to build stuff into them that is also wildly different. I can't give too much away, but the next GPG has an archetype article of mine... and it's one of the first things I ever wrote for EN Publishing coming out after later works.
2) Environments and Journey make the game way easier to run overland without just timeskipping.
The Journey System -remains- my favorite thing about A5e. It gives everyone some activities they're responsible for on their trip, it creates a real sense of adventuring being separate and unsafe from pastoral life (by making Safe Havens a thing), and it gives me lots of little hooks to play off of.
New feat that plays into making the journey safer? Awesome. New magic item to help you gather supply? No problem! New Exploration Challenges to viciously rip away your supply and make you wander across the wastelands of Athas in the hopes of finding good people to help you... or weak people to rob? Love it.
Journey plus a Hex or Square Grid map? -So- good. Fill in the spaces with the regions you want or just roll. Also: REGIONS. Conceptually it's just describing your environment as you go, but by giving it structure through Tiers and the like it makes it a lot easier to figure out where the local Fey Lord is.
3) Rare Spells
Come. On. Rare Spells? FINALLY decent loot for Wizards.
4) Combat Maneuvers
Just like Rare Spells, combat maneuvers give me fertile ground to play around. Wanna play a Spellblade fighter? Just slap together a Mystical Warrior combat maneuver set and have them pull out neat quasi-magical powers, then slap the O5e Eldritch Knight archetype onto the character. BAM. Lots of little magic and a few big magic effects.
5) Culture separated from Race
I know some people find it a waste of time, but it allows for some -truly- fantastic and simple design and I'll put it this way:
Would a High Elf Street Urchin living in Neverwinter have the same "Arcane Schooling" as if she were raised in Silverymoon? No way. Magic blood could be a way to explain it off, but wouldn't it be -cooler- to have her learn stuff that's more tied to Neverwinter itself? NEVERWINTER CULTURES. Various metropolitan cultures built around different aspects of life in Neverwinter.
You wanna play a fancy-pants hoity-toity High Elf? Cool, pick the Neverwintan Highborn culture. You wanna have your High Elf be from a disgraced family who grew up from a young age fighting for scraps on the streets? Neverwinter Street Tough culture.
VARIETY!
6) Reputation and Strongholds
FINALLY. A tangible understanding of just how famous my character is. Pairs really well with a level 4 Bard telling epic stories about the party.
And having Strongholds and Followers as part of the base game, rather than a later-released bolt-on system? Yes, please. My brand new cult whose whole goal is to collect the contracts and journals of warlocks to pore over their Books of Shadows for personal power needs to be able to build a hidden library under a Tavern on a budget.
We're not -that- high level, yet...
7) Minor Magic Items
Okay, so... there's stuff in the Trials and Treasures that you'd never find in a DMG. Like a book that helps you learn how to don and doff armor super fast. That's just -such- a minor perk... but. It fits certain characters. Like a powerful Myron warrior who oft enough finds himself at sea or ship and may need to quickly divest himself of armor if he falls overboard...
And even if it's -not- useful, it's still -neat-. Because it's a book you have to read over the course of 3 days to benefit off of and that Myron is SO EXCITED to be able to increase his list of books read to 2.
8) Press the Attack and other Baseline Combat Options
Tactical Combat is a ton of fun. It's also a major hassle. So having clear, simple, easily shaped in a theatre of the mind version of 3.5's various bloated maneuvers, and Pathfinder's even more bloated list of lightly streamlined individual maneuvers, with new very simple stuff on top? Freaking -Mint-.
Press the Attack, on it's own, could shape an entire character identity just as well, if not moreso, than Reckless Attack... because your target falls back, pressed, to negate your advantage by giving ground. Stumbling away until their fancy footwork falls flat. I LOVE IT.
9) Expertise.
Advantage was O5e's big game-changing design, bar none. Finally moving away from stacking endlessly larger bonuses against comically larger DCs. Expertise kind of brings back the bonus-boosting, but does so with a single growing dice that feels more fun to play with than trying to remember how many +1s your god-kobold has before he reaches infinite power.
Summary or TL/DR:
In addition to a few specific big systems, there's tons of little hooks and levers that -beg- for someone to come in and pull them all. To design new material that plays with them in interesting ways. And that shape a slightly different,
7 am Edit:
I was writing this while dog-tired from a long day... I have no idea what that last sentence was trying to be. I think I might've dropped off mid TL
R and woke back up, hit 'post' and gone to bed.
I think maybe it was...
And that shape a slightly different, but very layered, structure of gameplay design.
