Like many of you, I bought Diablo 3 on day one and loved it, right until I reached Inferno difficulty. Getting frustrated by the game's difficulty, I swiftly put the game, and my level 60 Barbarian, down. I dabbled a bit with the other classes (got a Monk about midway through Nightmare on hardcore before dying unceremoniously) and stopped playing the game entirely for several months, along with most other non-crazy people, for whom Diablo 3 was simply the hot "game du jour".
With patch 1.05, I decided to jump back in and see if it affected my modestly geared Barbarian at all. Much to my surprise, it did, and to great effect. Suddenly, Inferno was no longer a gruelling war of attrition, more about playing the itemization metagame than the actual gameplay. I was able to make good progress with startlingly few deaths. I cleared the remainder of Act 2 and swiftly mopped up Act 3 and 4 some time later, in a mixture of solo and co-op play.
If you don't know what patch 1.05 added and changed, check out the changelog. The addition of Monster Power seems to have coincided with a general nerf of Inferno difficulty, which to my understanding has happened gradually over the last few months, so my newfound success probably can't be entirely attributed to this one patch. Monster Power seems like a great change: it adds further difficulty tweaks with added rewards for those who are, at this point, horribly overgeared for regular ol' Inferno. For those people, the new Infernal Machine event adds a new challenge and goal to pursue. This is somewhat beyond my current gear level though.
Going back to Diablo 3 after playing some Torchlight 2 also served to remind me just how enjoyable D3's combat mechanics are. There's a real weight behind your moves that communicates your character's power to great effect. The skill system holds up well also - your loadout will radically change the way you play your character, and if your build doesn't work or you get some new items that make you want to adopt a different build, switching it out is as easy as returning to town and pressing a few buttons. Inferno, as it stands, is just hard enough to make you think carefully about what abilities and runes you want to equip, without making it so that only a select few playstyles are viable. They've finally achieved that difficulty sweet spot that was so sorely lacking in the original release.
In recent months, Blizzard's done a good job of listening to fan feedback. Legendary items have seen buffs and the addition of cool new unique effects, Inferno has been made approachable without anything but top-tier gear and incredibly specific builds and item drop rates have been improved across the board. This is anecdotal and may be completely incidental, but I found a Legendary item in Act 3, whereas I never found any Legendaries in my Act 1 Butcher runs on Inferno back in the original release.
If you abandoned Diablo 3 for reasons similar to mine, I recommend giving it another shot.