I played 4th edition nightly for about 4 years and had a lot of fun with it. I was also working two jobs and attending college which is really a testament to how easy this was to bring to the table if you bought fully in. Adventure paths that had every encounter mapped out and keyed with where to place monsters and special terrain, dungeons that were built using their Dungeon Tiles, and online tools to update/print out character sheets quickly. As for prep, since each combat took about an hour, you could get away with just reading the next few rooms and still have an entire night of gaming.
This way of playing D&D was pretty new and I think much of the first half of this version's life was trying to figure out how to best play it. IMO, this was either large 6 hours blocks devoted to exploring giant, pre-laid out dungeons (like a complex boardgame) or smaller 3 hour blocks where each session was built around a giant battle (think Final Fantasy Tactics or Fire Emblem).
What killed the game for us was a number to bad decisions made because D&D desperately needed to be a billion dollar franchise right away. One of the worst was selling randomized packs of cards that would give PCs "power-ups" for when they played at the table. As if any DM would let that fly... Another was to try and rope in the grogs by making an "other" version of 4E called Essentials that confused absolutely everyone as to what it's purpose was exactly thanks to vague promotional descriptions and two "Player Handbooks" that shared half the same information. The final straw though was not supporting their new Dark Sun setting via their online tools.
That seems like a whole lot of negative for a "+" thread, but I really wanted to drive home that many left not because the game itself was flawed, but because towards the end it was very clear they were laying tracks down as the train was moving with no destination in site. In other words, D&D was becoming a really bad investment, especially with that new game Pathfinder that just came out...
It was a great game for its time. And as someone that played a lot of 3.5, the design decisions we think of "odd" now, really were logical continuations of the "meta" at the time. Thankfully, the best parts of the system still live on through 13th Age and Pathfinder 2E.