Some of the things I will remember 4e for:
Exciting encounters! To parrot what others have said, many fun amazing moments were had in service of the adventure as we went along: knocking opponents off towers, dazing the big bad and causing his prime buff to fail (and thusly get thoroughly ganked), rituals around the edges of intense combats, dragon-riding knights of Bahamut driving a lance into the body-splitting psionicist, bonus actions that swing the tide of battle, and the controller making the DM (like me!) saying “You do
what now?”
Empowering DMs for awesomeness! In one of the first 4e adventures I ran, the big bad wrapped his chain whip around one of the PCs, pulled him in and body slammed him against his spikes, for damage and a knock prone. Rather than the players, as they’d done in 3e, going “Wait, how did he do that? Did he grapple? I get a +4 against that! Etc!” instead there were cheers of wonder for that neat trick. Letting the adversaries be constructed to suit the adventure, separate from any PC rules/etc, made it easy and fun for a DM to prep a game, and also allowed for that nifty creativity.
Empowering PCs for flavourful excellence! Each class was given licence to do cool things (tm), and do them often. Even PCs that did similar things (same roles) did them differently, making it easy to create an interesting story/style to RP alongside the action (and bleeding into the non-encounter portion of the game). Add to this the ease of re-skinning powers/classes, and it’s golden – like my Dwarven Runecaster (reskinned artificer), steeped in the lore of the FR mythos.
Being willing to eat sacred cows! While I don’t think every change turned out to be good ones or necessary, some were quite nifty, and I will remember the 4e team being willing to not be bound by previous editions.
A return to 1e roots: crafting/non adventuring skills! 4e removed most mechanical support for anything that wasn’t part of the adventuring skillset. While this gives great freedom, it wasn’t spelled out that it was intended to have that freedom, and a little mechanical nudge helps, so I wasn't a full fan of this one (hence my Trades & Professions supplement).
A return to 1e roots: Hit Points! If you read what the 1e PHB has to say on hit points on p34 (including the delightful “it is ridiculous to assume” wording), 4e took it to heart in its mechanics, both with the (perhaps poorly named) healing surges, martial “healing”, and more. And while what HP represented also didn’t change in 2e or 3e, 4e was the first to expand and play with what could be done in that framework to bring about new options.
A return to 1e roots: game design! Similarly, reading Gygax’s statements on p9 of the 1e DMG about what the philosophy of the D&D ruleset was, and 4e plied along that path.
A great effort to create balance in the force! Not every character was the same yet there was a great push to allow everyone to be an integral part of the action across the boards and across all levels.
Skill challenges! I lucked out – the first example I read about skill challenges (done at a pre-4e event by Chris Perkins, IIRC) set the tone in my mind on how to use them, which may well have been much better than how they were executed in the DMG and (especially) in the encounters modules. Because of that they worked out very organically and fun in my games, and the players usually didn’t know they were in something called a skill challenge (I used it mostly as a narrative framework rather than a metagame obstacle).
Battles of speed or not speed! In my high level campaign, battles took just as long under 4e as they did under 3e; but low level battles often also took about that long. If the battle was narratively interesting, it wasn’t an issue. If not, it could feel like a schlog and it took some time for me to alter how I ran them to get ‘em moving along more quickly.
Amazing stories and fabulous adventures and sweet RP and tense dungeoneering! Just like every other edition of D&D I’ve played.
Many characters I wanted to play! And still might!
The edition war that went nuclear! When I started gaming 20+ years ago, the lament of most D&D players was how they were ostracized, ridiculed, harassed, teased, belittled, dismissed, and shunned for their like of this hobby. With the intense dislike by some of 4e and the ensuing edition war sniping and hyperbole, I learned that gamers can be just as petty, mean spirited, and myopic as the “jocks” they decried.
peace,
Kannik