>Massive, free update to game with no sub fee
>Ton of new content, including the oft-requested ladders and leaderboards
>More challenging endgame content for organized groups
>Shitload of bugfixes and buffs to nearly every class
>Huge fix to AI/pathfinding for minions
>"but but... muh offlines!!!!"
Free? No, only if I purchase the expansion
Wrong! Your game is automatically patched via Blizzard desktop launcher, and you get the benefit of all the bugfixes, class tweaks and pathfinding improvements even in the base game (most of those pathfinding issues were aimed at WD, which is a class playable in the base game). The patch is free, in every sense of the word.
to a game I already paid premium dollar for and was broken for the entire first year of play.
I'm actually quite sorry you paid for the game on release, as it was a total shitfestival in 2012. Loot was terrible, legendaries were terrible, auction house was terrible, story was terrible, class viability was terrible, difficulties were skewed to *heavily* favor ranged classes, list goes on. But the loot 2.0 patch (that was also a free patch, similar to this one) came out and fixed... pretty much all of those problems. By axing the AH and introducing "smart loot" that favored your class, the majority of items you got were upgrades. Even a character who had been playing for a year by the time loot 2.0 came out saw a steady stream of upgrades off the bat, because class-tailored loot was an amazing change. They also increased the droprate of yellows and legendaries, so instead of getting majority blues, occasional yellows, and never oranges, you got majority yellows, occasional oranges and even a few greens (which I'd never seen a single one of before loot 2.0 hit). This, again, increased the quality of the loot acquired, and with the ongoing project to give unique legendary effects to every legendary in the game, many of those are now cornerstones of powerful and varied builds for each class.
The story, unfortunately, is still an absolute joke. Everything from the butterfly princess to the "master tactician" who watches you single-handedly stomp his entire army into the dirt and taunts you the whole time just reeked of *terrible* writing, and now that the majority of the game is actually pretty good now, the story sucking so much sticks out like a sore thumb. The Reaper chapter story is a slight improvement, mostly because Malthael shuts the fuck up and doesn't actively taunt you the whole time, serving more as a villain in the shadows, letting you learn about his history and motivations through collected journal entries before the final showdown. It doesn't come close to rectifying the total joke-on-wheels plot that encompasses the previous acts, but it's a nice step away from it.
I came back to the game in 2014, after getting the base game free (so I never felt "betrayed" by blizzard when d3 sucked at launch, I just didn't like the game and stopped playing). The loot 2.0 changes, the difficulty level changes (content scales by character level now, offering a much more customizable challenge), and the removal of the auction house catapulted the game's quality up to what I had come to expect from Blizzard games - I was able to finish leveling all my characters to 60, and played quite a bit on my Wizard to gear him up and see how the "endgame" played. Based on the amount of fun I was having, I decided to shell out $40 for the expac. After leveling a crusader to 70, and all my original characters as well, I settled on WD as my new main and played hundreds of hours more - joining groups to speed clear bounties, farm mats for legendary crafting materials, and even participating in the great Rift It Forward community as a runner.
The game has changed. It's an entirely different product than the shlock you saw at launch. So much of what made it bad was gutted out entirely, and replaced with superior systems (or no systems, in the case of the AH), and the introduction of bounties + rifts added a lot of replayable content, enjoyable solo or with a group. Diablo 3, in its current state, is every bit the game Diablo 2 was - the only noticeable difference in gameplay is freedom in skill/rune changing removing the requirement for additional character grind that D2 had. Some people found that kind of theorycrafting gameplay rewarding, where they'd try to take a fresh character up through Baal to see if a weird build would work, but those were definitely in the minority, and everything else that made D2 fantastic can now be found in d3 (farming, legendaries, group content). There's even PvP, for the few people who thought d2 PvP was ever any good (although they're fucking delusional).
If you want to hold a shitty launch against a game for all time, that's up to you, but keep in mind the game is nothing like that anymore. Since you already own it, why don't you try it out? You don't need to buy the expac to see the majority of the great changes they've already made. The expac just offers some new wallpaper and bigger numbers, the core game is the same even at 60.