I both played and DMed it. And guess what? I loved it. But like any editions it had good and not so good points in it.
The really good
1) The ease of learning. It was really easy to teach the game to a new player. Much faster than any previous editions (even 5ed is not as easy to learn).
2) The preparation time was short. You could build encounters and adventures in a moment's notice. It was so fast that I could prep and 8 hour session in about 1 to 2hours depending on how much details I wanted to write down.
The good
1) Finally the martial classes could compete for damage with the casters. No more CODZILLA!
2) Clerics/Healers had something to do beside healing or CODZILLA!
3) The cantrip were now an at will power. This is the single most impressive thing that 4ed brought. Yes, 3rd editions had them but they were limited. Now the cantrips were usable by the casters. They now felt like true user of magic able to weave arcane power at all time. This was both refreshing and a nice way to make sure casters could always do something useful.
4) Rogue like class were deadly! Critically so. Never turn your back on a rogue was never truer than then.
5) Monster stat block were usable from the get go. No more : Ok, this dragon is also a 10th level caster... which spells should it have....
6) The minions! This was a great idea! It was almost like a movie where the heroes hack their way into the "minions" like a hot knife through butter and finally gets to the real elite guards and now must do a real fight. Used correctly and sparingly they were a great narrative ploy. But they also led to a problem that you'll see further down the post.
7) The importance of terrains was crucial and made up for really good memories.
The not so good.
1) Roles were a bit too MMORPGs. (Dare I say WoWesque? Ruin Explorer?). I was a competitive player in the days and the difference between a tank and a defender is barely noticable (mechanically different yes, but the end result is the same. This is what I called aggro through maneuvering denial). Though the healer role isn't really comparable to the leader it can be said that it is close enough for the untrained eye to be treated as such. DPS and CC are there from the get go. And a CC can be a DPS too. Just as in a certain MMORPG. But, again, it was not such a bad thing.
In fact, it was helping the young (new) players to learn the game that much quicker. I was still teaching how to play D&D in a Youth Center and it helped lowering the learning curve by a lot. They could all relate to the WoW roles.
But It was a bit too determining for a character. Role swapping can be fun but once committed to a role, it was a lot of work to get out of it. (well, you could but at one power change per level...)
2) Feats. As in 3.xed, feats were a bit too prevalent. I much prefer the 5ed approach to feats. It was a good customization of character but again some feats were almost a no brainer and you were supposed to take them. If not, then... But the problem was not as prevalent as the 3.xed (the tax feat...) so I put it at not so good.
3) The additional PHB... One PHB ok, 2 PHB? Mmmm Okish. 3 PHB? You're trying to squeeze money out of my pocket. 4 PHB (what do you think Martial, Arcane, Primal and Divine power books were?) That is way too much for an edition that was so young. Too much choice only leads to confusion. I Stick with only the first two in my games. But I had the rest, as usual. I just didn't like them enough to incorporate into my games.
The Bad...
1) The adventures. If they wanted to kill the game, it was the way to go. Some of you might have had good times with the published adventures but we did not. In fact, I recognized their design flaws almost immediately and I fell back to create my own adventures very fast. This avoided a lot of pitfall that other DM I knew fell into.
2) Skill challenge. A good idea. A reallllllllllly bad mechanic.
3) The monsters. Their stats block were easy to memorize (The same problem is there in 5ed) and it led (in some of my game) to a meta game where the players were trying to distinguish which monsters were minions and which were not. This is why that I said (earlier) that minions had to be used sparingly. Otherwise the players would divide their attacks among any number of opponent to "fish" for the minions. In hindsight and in retrospect, minions should have required about two average attack damage per tier to be destroyed. They could have been some kind of lesser opponents that would hit a bit less, were a lot less tougher than their normal counter part but could act as a filler for a number of opponents. I am still unsure on how I would've implemented it but I'm sure you see the direction I would've taken.
4) The HP bloat. Again, more HP leads to needlessly longer fights. We do have this in 5ed too but since the number bloat from cumulated spells and what not isn't there anymore this is less of a problem than in 3.xed.
5) Tactical combat. About the same as in 3.xed, combat could take a long time because of the too many different tactical options/combinations. The streamlined version of 5ed is better.
Again, I really enjoyed the 4ed. It had strong points going for it. I was not present in the forums at that point. I was working long weeks at our power plant and I was working as a volonteer in our local youth center in addition of my own gaming groups, my family and my WoW games. I took a three year iatus from DMing as our factory closed and I went to a different region to work in an other power plant. I almost played Wow exclusively for 3 years then our factory reopened and I went back to my home region and restarted my groups. From 2012 to the start of 5ed we played both 4ed and D&D Next (the playtest versions of 5ed). (I still have the files from 2013 up to summer 2014

). So yes, I remember 4ed and I really liked it.