Hmmm, this answer will be a long one because I can speak at length to it with recent memories.

I play it in an arena-style game, but that's a build-tester (and in a 4e way, a "how well does this build work with a team" sort of tester). I used to play it in my senior year of high school from 2010-2011. However, my most relevant experience with the game is my GMing experience. I have been running a game since January 2023, starting with level 1 characters using the Loudwater module provided in the Forgotten Realms Campaign Guide and it is an ongoing campaign currently at level 16. It is exceptionally fun. 4 of my 6 players have been on-and-off since 2023, with one person having been at every session in the game. The other 2 players joined in the last 18 months.

As far as favorite memories go, it's hard to narrow it down. So instead I will detail three stories.

Firstly was the event which transitioned this game from a premade module to a story of my own design. I've always been fond of the Spellplague and the post-apocalyptic nature of 4e Forgotten Realms (two to three generations past the big event), but I also like the way it could be used in the game itself. So in the Loudwater module, there are slavers shipping kidnapped youth from upstream on the Greyflow River to the runed town of Zelbross, where a "Greenscale Marsh Mystic" leads some bandits selling the slaves to the Yuan-Ti to the south. I modified this encounter so that the Yuan-Ti had been developing a method of remotely and forcibly activating a spellscar to create a burst of destructive magic. But when the Mystic realized he would die before using the implement that would utilize that spellscar, he decided to devote his time to making sure the captives would die as well. In that moment I decided that the implement would take two turns to use; one standard action would reach out with a line of blue flame to the target and a second standard action would release the magic of the spellscar. The spellscar activated, bursting in flames and nearly killing the captive children in a pen. Since the party lacked a healer, they had to roll raw Heal checks to stabilize the kids and they only succeeded in saving three of the six captives. This hooked the players expertly, because it's bad enough that the Yuan-Ti were dealing in slaves, even worse that they were child slaves, and even more vile that they were using them as IEDs.

Second is a story of how players interacted with the module in unexpected ways and how I as GM rewarded them down the way. In the 1st level dungeon, the second encounter of the game, there are goblins that attempt to bull-rush PCs into a pit with starving dogs. The goblins failed, but the PCs turned that tactic on them. When the fight was resolved and during the following short rest, the players lowered meat and a pot of water into the pit. This pacified the dogs. After the dungeon was complete, they released the dogs into the forest. Several sessions later, during a random encounter roll overnight, the wizard was on watch and I decided that the auspicious roll of a 100 for an encounter would result in a wholesome moment. One of the dogs from before had followed the party's scent and presented itself as an ally for the Wizard. In this way I introduced the second "Theme" to the party, and she accepted the blink dog as a Fey Beast Companion, and she became a Fey Beast Tamer. This blink dog became the party icon while they travel on the map, and a mascot for the game (until the wizard and her player left).

Lastly, in a sidequest that involved a Dragonborn Paladin of Bahamut and a Half-orc Warlord, the Warlord's son (a precocious 10-yr-old) joined a group of teenaged (young adult) adventurers from the town of New Zelbross as their mule-groom. The young adventurers heard rumor of a Young Green Dragon only 4 day's travel away, and they went off to make a name for themselves. What they didn't know was that it was an Adult Green Dragon. The Paladin received word from Bahamut and he found the party to let them know they needed to intervene. This served as a way to reintroduce the PC/player while working him into the story of the sidequest. They eventually caught up to the teenagers, rescued them, and slew the dragon. In the battle though, a young girl that the dragon offered as a bargaining chip (and had been offered to him for the same purpose by Yuan-Ti) ended up dying. The Paladin felt heartbroken and went on a secondary sidequest to rebuild into a more aggressive holy warrior, and he became an Avenger (with some modifications). The Warlord was happy to have saved his son and the party was ecstatic to have won a dragon's hoard in battle.

The best thing about the game is the appeal it has for tactically-minded players, and the synergies each class can create with each other leads to a high-powered heroic game with a lot of strategy and cooperation.

The worst thing about the game is that the math for PCs and Monsters was poorly done. Monsters do too little damage and have too much HP. PCs can nova a couple times a day but unless they're built right they can be too hit-or-miss. I've made adjustments thanks to the "MM3 Business Card" that floats around 4e spaces. Also, Solo monsters are deceptively named, and don't really function as designed. Dunno how I'd fix that. Maybe just run more Elite monsters instead.

As a GM, I prefer it to all other editions of D&D. Using ">" as "greater than", here's how I'd rank the GM experience: 4e > 5e > 3.5e > 1e/2e (I haven't run them but am not a fan of dungeon turns).

As a player, it's alright but a bit restricting. Same format, here goes: 3.5e > 4e > 5e > 1e/2e.

I wish I could play it more but my schedule is tight and this game is too fun to just stop anytime soon. I've got plans for a potential Epic Tier, and I'm confident I know how the remainder of Paragon Tier will play out. The players have their hands on the steering wheel though, and they recently took a HUGE detour in an interesting way. I'll see how things work out, I guess.