This game is a little more complex than what some people may percieve going in, but on the whole, its an incredible and rewarding addition to D&D.

Biggest Pros:

1. Heritage, Culture, Background, Destiny replace race and background in terms of your character building (i.e you can have a dwarf who was raised by elves, who gets dwarven racial feats, but elven cultural traits. Stat boosts come from background (which you can read to be more like an occupation, or just 'what your character did'), which makes MUCH MORE sense than purely racial. What you do should be more important than what youre born as.
2. The exploration pillar. My goodness its totally rebuilt and better than I thought possible. It's mechanically sound and gives the ranger an area of expertise (while theyre still very useful inside any city as well). If you don't use exploration, at all, then youre missing out on a really great system. The exploration bullet points apply more to the
3. The character options have been improved, and martials feel awesome. I love the changes to Fighter, Monk (adept, in this system), Ranger, Bard (instruments have a purpose!!!), Sorc and Wizard. I havent gotten to try much else, given its only been out for a month.
4. The Marshal class. I think people were saying its "4e's battlemaster?" I did not play 4e, but if that helps you visualise it great. Its a martial support class, which can use one of its attacks to compel one its allies to attack instead. This is a unique class, and I love the idea of a support like this. One excellent feature is "Help" as a bonus action
5. Spells, and RARE SPELL Variants. Special variants of spells that do unique things.
6. The "Rattled" condition, and the reworking of special maneuvers (shove, grapple, disarm) to only use one of your attacks (meaning at higher levels, it can be beneficial to to use a special maneuver instead of 2 attacks, since you dont have to sacrifice all your damage that turn.
7. Theres a lot more, but Strongholds, Followers, Strife and Fatigue, and Crafting all have great reworks/additions that make them important.

Biggest Cons:

1. The character creation process, because youre probably coming over from 5e, is extensive, since you need to re-learn a few things, and there are so many options for Heritage, Culture, Background, and Destiny. You might need an extra long session 0.
2. If you run a one city campaign, the exploration pillar might not be used at all, which, imo, may kneecap this system. iMO the class and fatigue/strife things are well done enough to subsist, but I think Rangers become pretty meh in a "one city campaign" scenario. Exploration and journeying is so baked into the idea for this system, I think its important to include it.
3. The book is meaty, but the journey activities section is totally located in the DMG (trials and treasures) meaning the players dont know about that entire aspect of the system, until you can work it out with them.

Overall, its a super strong system with a lot of positives that you can structure a campaign around to make it a superb experience.

So i'll keep this brief; while this is structured for A5E, the level up system and all that, its totally backwards compatible with the original 5e system. And tbh, while the other books are great, you can find some questionable decisions in the other 2 books, (Adventurer's Guide and Trials and Treasures.) Not everyone can agree with EVERYTHING that everyone does.

But then theres this book. The A5E monstrous Menagerie is so good that I can genuinely say its a better monster manual in every fashion and aspect. A5E has significant fixes to Challenge Rating system, and makes it understandable, and this can be kept in original 5e too, since the CR system was always a mystery. So, this book can be used in both systems Every single monster type has unique qualities. I'm going to use the Chimera as a review subject, because its a classic creature. This book goes into detail on aspects such as:

1. Legends and Lore, Roll an arcana nature check, and you can see what you have heard about the creature, with two different options, one for a DC10 and a DC15.
2. Signs: 4 options (d4) here, some creatures have more. 'Signs' are clues you can use to know that a certain creature is nearby without giving away everything. Chimera's include ' charred trees', 'tracks with a mix of big cat and hoof prints', and 2 more options. These signs are not totally unique to the chimera, but thats the point, theyre clues, many things can have them, and youre just trying to help clue your party in.
3. Behavior: what it would be doing in the moment you see it, a d6 option here, including "Two of its heads are fighting with one another" or "flying overhead looking for prey."
4. Sample Treasure
5. the statblock, of course
6. Combat Tendencies
7. Variants and regional chimeras. Chimeras that differ based on the region there from, like the sea chimera, which seems to be a lobster-shark-narwhal. theres 5 more variants but you get the point

This book I can genuinely recommend no matter the system, its just so good.I love the easy to understand CR system is, and all the extra detail that was put into each creature, making them all unique and very improvisable.

Journeying and Explorational rules, combined with regions, make the Explorational pillar one to behold, finally restoring the third pillar of D&D. Journey activities give players something to do while traveling, Exploration challenges set up unique activites that dont have to purely be combat. I love the fact that not everything is combat, and they still handle combat very well!

This book has plenty of tables to roll on to make each exploration very uniuque and fun, including Social Encounter tables, travel scenery, weather, region tiers, its really incredible. Combined with long term effects like Fatigue and Strife, it works to make your A5E D&D experience extremely memorable, and is equal parts preparation and improvisation.

Great book.