You can download Heroes Against Darkness for free, or buy a copy of it from this link.
I played 4th edition Dungeons and Dragons from 2008 to late 2009 / early 2010 with what was at the time my long-term roleplaying group. I hate edition warring, but we ended up abandoning 4e for a couple of reasons. First, the supplement treadmill became overwhelming, especially since all the changes were integrated into the character builder. There were new books almost every month through the early years of the line, almost all of them adding new powers, new species, new classes, new paragon paths, new epic destinies, new magic items. Evaluating this material ate up hours and hours and hours of time, and required the character builder program to stay on top of it, which only one of my group had. We'd had similar problems with 3.x, and it had pushed us to play Iron Heroes, Arcana Unearthed and other variants of D&D.
Second, we found that the game encouraged us to use powers, rituals and skill challenges to resolve almost all problems, and particularly with skill challenges, we kept on creating more and more types of skill challenges, trying to find a system that worked for us. We had similar problems trying to stage certain kinds of fights on grids (like chases on horseback). It felt like we were constantly racing ahead of the system and dragging it along. I don't think we ever played a straight, stock version of D&D 4e, and it made discussing my games with other people, regardless of where they stood on 4e, very difficult, since the attitude I got back on both sides was to stick closer to RAW. At a certain point, the errata on core pieces of the system like page 42 of the DMG (the one explaining skill challenges) had become so extensive that I just lost interest in using the 4e ruleset.
Third, we tend to play campaigns that don't fit well into the at-will / encounter / daily structure of power use and while we did a bunch of work to try to reconcile our style to the game, in the end it wasn't a comfortable fit. We tended to play with a highly variable number of fights per session, which meant that there were some fights where the PCs could blow all their dailies because it was obvious this was going to be the only fight of the day. Outside of set-piece dungeons designed to provide the required number of encounters in the requisite amount of time, we had to fiddle with XP budgets and fight set-ups extensively, and I don't know that we hit the sweet spot consistently, though there were a few really grand fights.
I mention all of this because Heroes Against Darkness is a 4e heartbreaker, and a really good one. It removes or diminishes the parts of 4e I really didn't like, while preserving its more interesting features. The obligatory grid is gone. The intricate sub-game of optimising characters, choosing feats, paragon paths etc. is gone. Skill challenges don't appear. There are a few mechanics related to encounters, but they are softened, and in general, where 4e hardcoded play expectations into the rules system, either overtly or subtly, HAD softens them to incentives. For example, PCs can take multiple short rests in a row, but each one takes 4 times the length of the previous one. PCs accumulate bonus experience for each encounter beyond the first that they plow through in a single day. There are lots of little tweaks like this that I really like. The GM advice chapter is also pretty meaty, and I'd feel fairly comfortable giving Heroes Against Darkness to a new roleplayer as their first adventure game. There's even a chapter on making the mechanics more like earlier editions of D&D (variable HP, harder healing, etc.) for those who want it.
There are two main downsides to the game, one serious, one not particularly serious. The not particularly serious one is that there's some extraneous swearing in a couple of chapters. I'm not a prude, but it kind of comes out of nowhere and doesn't serve much purpose. The more serious one is the underdeveloped skill system. Skills are mentioned in a couple of places: Each class has some suggested skills they should have, and there's a big list of possible skills, but the actual rules for skills are totally missing, from how many skills characters should have, to how and when they select those skills, to what skills do or how one uses them, to how one gets more. As a quick set of house rules, I'd imitate 4e somewhat: Having a skill would grant a +5 on any checks related to that skill. Character would select say, four at the start and could add another every other level.
Heroes Against Darkness in general has the feel of 4e done right. I don't say that as someone who hated 4e and wanted it to be fundamentally different, but as someone who played it and felt that the game didn't live up to its own promise. If that sounds like the kind of thing you'd be interested in, go check it out.