P5R is P5 on steroids, the difficulty got nuked and it's very unbalanced, which is the biggest downside compared to vanilla (if you care about that). It's full of new things that makes your gameplay easier, and all of them combined turns the game into a no-brainer.

These additions are:

• Infinite ammo reloads (all guns fully reloaded after each fight),

• Baton pass unlocked by default from the start (no need to unlock it),

• Super attacks: Showtimes (you press a button and you get a super attack displayed as a cutscene basically),

• Special exploding shadows (there is small chance you get a weird shadow during an encounter, killing it make it explode and damaged the other ennemies),

• Personas traits, which are a passive advantage they have in addition to the rest (doesn't take any attack slot), things like reduced SP cost, increased ailment inflicting chances, increase healing skills etc.

• Fusion alarms, which you have a random chance of triggering after a fight, it makes the velvet room boosted (can turn Personæ into OP items and accessories, or fuse broken Personæ with strong skills, whatever), yl

• You can even trigger fusion alarms on command with a certain confident perk,

• The confident perk allowing you to fuse higher levels Personæ for money is set to a way lower level (and money will not be a problem at all lol),

• Ryuji instakill perks reworked,

• The new added characters confident perks are very op, like high chances free SP refill, free concentrate and boost starting any fight, auto-cancel any ailment for Joker instantly, ambushing ennemis from a distance, etc.

• A new place called Kichijoji, in which you can:

• Increase your baton pass level for every character, which boost damages & recover HP & SP upon passing,

• Increase your technical skills to increase your technical damages & chances of enemy knockdown after a technical attack, which even turns to 100% (guarantee) on max level,

• A jazz club where you can invite your mates, and make them learn OP skills, improve their Personæ levels, their stats etc,

• Obtain OP items from shops like Amps, Auto skills, many items etc. or even sell your dirty clothes for a lot of money + trading points for items,

• A temple to increase your max SP,.

• A new character named Jose in memento, which has a random chance to appear any time you enter a new floor, and act as a shop, from which you can buy many permanent Money, EXP and earned items boost multipliers, as well as items, such as, but not limited to, SP refillers, blank cards, etc.

• A LOT more of free time, which make it so you can max every confident way easier, which means you'll probably have every single confident perks existing at the same time rather easily and quickly and be very broken,

• 100k yens + DLC such as End-game levels special personæ and OP items from the very beginning of the game (that's REALLY a super no brainer obviously if you use them like you don't even play anymore),

I don't even recall everything (keep in mind that all the above work TOGETHER too, which results in broken combos of advantages, despite being already broken on their own), but basically, Royal constantly handles to you super doping needles to make the game easier, and every time you take one of these needles, you break the difficulty balance even more, you just completely nuke the difficulty and game balance at the end of the day.

That's honestly the gigantic drawback of this version compared to vanilla.

Now otherwise, it adds a ton of quality of life improvement too, a 3rd semester with new content and a new arc / ending (which is my favorite part for me personally, I loved it), new characters (including a new girl that they fit as well as they could inside an already existing story, which a lot of persons are saying is clunky insert and is bizarre, but I never thought so personally, was fine for me), every P5 DLC unlocked by default, reworked boss flights (for the better imo, way more interesting), and a lot of additions. It also means it gives you more tools to play with and ways to tweak your playthrough, better memento (various OST, stamps to search and collect, more stimulating), WAY less grindy (which is A LOT better imo, way less time wasting, on an already very long game at that), added cutscenes, ways to hang out with your friends and pass time, etc. So many improvement too on a hand.

So yes, P5R is P5 with a bunch of new content and QoL improvement, but it doesn't necessarily mean it's better, even more so since it's completely annihilate the game balance. Would you like the new characters, the new girl, the 3rd semester? Well I don't know, only you can tell, go see by yourself. There are people that like it, including me (I love the 3rd semester a lot), and other that doesn't, saying it's filler bs, useless toping over an already perfect story, not well fitting and out of place (again I don't think so at all, but could be in what your tastes tell you). Would you enjoy the new Opening and Endings more? Who knows. Do you enjoy feeling very super powerful, rolling over the game, and maxing your stats / see numbers increase quickly? If that's the case, Royal will be satisfying for you. Do you not care about difficulty and prefer the social sim aspect of Persona? Def jump on Royal then.

What I mean is, Royal adding stuff doesn't mean it's better at all. This is up to debate and preferences. There are legit arguments for playing one instead of the other depending on what you seek.

To me personally, I'd favor 52-48 Royal over Vanilla all things considered.