Before you Buy:
• Age of Empires I: Definitive Edition (AOE1:DE) is a remaster of the classic AOE1 game using its original engine and has all the DLC but still has it's original quirks and poor AI pathfinding.
• Age of Empires II: Return of Rome (RoR) is a DLC for AOE2: Definitive Edition that imports AOE1 all the civilizations and mechanics and the core campaigns (while adding 1 new civilisation and 3 new campaigns) into the AOE2 engine.
• Both aim to deliver the AOE1 experience but AOE2: Return to Rome significantly improves feel, features, and integration.

AOE II: https://store.steampowered.com/app/813780/Age_of_Empires_II_Definitive_Edition/
AOE II: RoR : https://store.steampowered.com/app/2141580/Age_of_Empires_II_Definitive_Edition__Return_of_Rome/

Note: This is my first foray into AoE1. Playing simply the tutorial I found myself alot more comfortable in the AoE2:ROR DLC. My recommendation is to start there from a campaign perspective. I can't say for multiplayer.

AOE is a classic, but the Definitive Edition lacks a lot to carry that name.

Most people buy this game to experience a slice of the past. Basically all what they want is the same old game now playable in 16:9 and optional improvements that can be turned on and off, be it graphics or gameplay.

What do they get?:

The campaign is not playable with classic graphics. Classic graphics sounds and music are only available in custom game mode.

The new graphics, music and sounds are quite okay, but they don't come even close to the old atmosphere, which nailed that Stone Age feeling. It's not even only nostalgia, the old game simply looked great: the colours used, the overall atmosphere of everything, which can be summarized in one word "Wololo".

All of that is an important part of the 90's early 00's . Not giving the player the option to dive into the past is simply a very bad decision.

For people who want at least the classical music when playing with modern graphics:

Click on Age of Empires in your Steam Library and Browse to "Local Files", go to the Assets folder, then Music folder. Make a copy of the files in the Music folder, and paste it to some free folder for backup just in case you mess up something. Then go back to Steam into the Classic folder. Copy the files from the Classic folder into the Music folder, let them be overwritten. Don't worry about the extra music file. Finally delete xMusic11 to xMusic15 to get rid of all modern music.

There is also a very good guide "How to play with new graphics, original soundtrack and sound effects" by Gnome, for those who want to go deeper.

Nostalgia overflows for this 1997 game, which I have fond memories of from when I was a kid. It plays well, and the multiplayer is a lot of fun. The campaigns and single-player modes are a bit weird and unbalanced, but still enjoyable to mess around with. The strategic aspect, at least for me as a total noob, feels a bit odd - since the game largely revolves around either rushing your opponent as quickly as possible or rushing for gold. Despite all its flaws and inconsistencies, I still have a soft spot for this game and really enjoyed my time with it.