I tried 5E too.

Admittedly, I took a long break from this blog. I had a lot of life-changes over the last couple years and didn't have the benefit of being around my accustomed people. But I still got a little gaming in.

In this interim, I got a chance to try Fifth Edition. it was only one session with a group that I dropped into. But it was a good chance to look at the rules and make a character and try the rules.

In short, here are my impressions. Let me restate that 3rd Edition is my main basis for comparison.

1. Mechanics: The system is essentially the D20 system. But the mechanics are significantly unified and streamlined. Good.

2. Power levels: Characters are both more powerful and harder to kill. I think the power-creep has gone to far. But certain aspects make sense.

3. Forced roleplaying: There are actual mechanics meant to inspire "roleplaying." They suck. Maybe they are a necessary crutch for some. I don't know.

4. Me hating other people's fun in a petty sort of way: Exotic character races and bizarre prestige classes are normalized and made mundane and thus irrelevant. This contributes to power-creep and to a blandification-of-the-weird. It legitimates the sort of self-indulgence which I find to be in poor tastes.

Mechanics
Like 3rd, 5E has us rolling a d20 and adding a modifier to beat a Difficulty most any time we need to ask a question of the universe (aside from damage rolls.) The difference is that the classifications of different sorts of rolls has been pared down, lending to more simplicity.
For instance, saving throws and skill checks are both simply "checks." I like the elimination of Saving throws as a separate category. In 3E, all saves had to be classified as either Fortitude, Reflex or Will, modified by Constitution, Dexterity or Wisdom respectively. This gives an odd extra value to those ability scores. It may have balanced out these states, but it was hardly elegant.

Skills remain. But their sheer number has been pared down.
(Skills are a sticky wicket when you are designing a system. ie. shouldn't someone with Profession:Sailor also be able to Use Rope? Or if you are trained in Medicine does that mean you know about medicinal herbs, or how to operate an fMRI scanner? Medical tricorder? And can you perform dentistry in a pinch? Should the system count those as separate skills? Wouldn't that be a little too gritty? Personally, I think a strong system should account for widely different technology levels and their interaction, which necessitates a more complicated system that one where Pre-Industrial Iron Age is the default)
Anyways, 3E had like 30, 40 different skills, not counting the unlisted ones which count under Profession or Craft. It errs on the side of being too finely parsed. 5th takes this down to about a dozen and is better for that.
Also, rather than having an allotment of skill points, and a to-hit bonus, characters are either Proficient in an action, or they are not. Proficiency in a field grants a proficiency bonus, the magnitude of which goes off a character's level. Whether the proficiency applies to a craft or a weapon, the bonus is the same. It's simple. But it makes sense. My gripe is that a character's skills are more or less locked-in at character creation, and there's  little room for customization or shoring up  weak skills along the way.
Also the proficiency increases in chunks every 4 levels or so, rather than incrementally with each level. Why? Not sure I like that.

5E adds the feature of rolling with Advantage or Disadvantage. Basically this provides the DM a way to adjust for the situation and say "Ok, that thing you want to do will probably work because of such and such." or "Ok, you have some serious stuff working against you (like trying to sneak in heavy armor), but you can still attempt it if you want."
The subject rolls twice, and takes the higher result if there is an advantage, and the lower result if there is a disadvantage. This saves the DM from having to arbitrary modifiers on the fly. Arbitrariness is built in, but is less debatable. I think I like this mechanic.

Power Level and creep:
3E might be a little kooshy, but there's still plenty of room for players to feel threatened and vulnerable at low levels. 5E makes this even worse.
I played a fighter with an archery specialization. The fighter has an ability called Second Wind which recovers HP once, and recharges with a rest. It basically doubles a fighter's HP, creating what might feel like tension, until you remember to use the ability which heals you for free.
Another big difference is that magic users can use cantrips (0th level spells) without limit. This wouldn't be a big deal in 3E, where cantrips are spells like Read Magic or the one that deals d3 damage to undead. But 5E includes cantrips which deal d8 damage, at a distance without limit. This makes for a big increase in the damage-dealing for low level spell casters.
This buff for spellcasters seemed extreme to me. But in terms of damage capability, it's comparable to what a character with a bow might deal. And it makes more sense than in 3E where spellcasters are forced to double as crossbowmen if they want to remain effective without burning spells.
In a game which is essentially about fighting monsters, it makes sense if you want magic users to actually have something to do in combat. So I can't object too much.
I'm sure there are other instances of how non-combat classes have been turned into combat classes. but I haven't discovered them yet.

Forced "roleplaying:"
As part of character creation, 5E asks you to choose a "bond," "flaw" and "ideal" for your character. There are about six of each for each class and you are supposed to chose a trifecta to guide how you play the character.
The problem is, once you make these sort of details part of the game system, they become subject to a form of min-maxing; choosing what will hinder your character least and off the most benefit.
By mandating these elements of character background, 5E might discourage players from creating characters according to their own inspiration.
Also these books are by Hasbro, and have to be politically correct. So the options the basic rules give you are pretty boring. For instance, I had to invent a flaw for my character: "Dislikes women." I'll spare you the gory details of his his background story.
I can see how some players might need this sort of structure to introduce them to roleplaying. But I think there is more hindrance than help.

I'm a hater who hates fun.
I just think there's a sort of breakdown in the game when a player can say their character is a half-dragon with a horny lizard-head and a breath weapon, and there is an expectation that the character can walk into a town and an inn with the humans and the halflings and everyone will act like this is totally normal. At that point, the game has seriously damaged its potential for weirdness and wonderment.
And "dragonborn" are default playable race in 5E. Thus informing the "default" D&D setting.

Also, the character-customization which would have been handled through feats and prestige classes are rolled into class progression. (We never got into prestige classes anyways. Why bother when you can multiclass?)
This forced branching of character archetype only creates and illusion of an individualized characters, when in fact, the available paths have only been more strictly delineated,
.
All in all, I appreciate the mechanical simplification in 5E. But at the same time, it offers even more of the shallow, indulgent fluff that made me run to basic. With one hand, 5E caters to the player's desire for an "cool" character. but with the other, it creates limitations that hobble creativity.