5th edition does a lot of things right. Curious to hear what peoples' biggest issues are with it.
1. HP scaling is an issue as I think you start with too few and end up with too many. The should have normalized starting HP and per level growth a bit better.
2. Subclasses are great, but I'm actually not sure I like them more than prestige classes. As time goes on, subclasses are starting to feel more restrictive and "forced" while prestige classes feel more loose and flexible. Also, there's inconsistency in design scope between classes and subclasses. As an example, the D&D cleric is really overdue to be overhauled to make it thematically broader so it can hold a lot more divine/priestly archetypes. This is part of the reason why people question the existence of classes like Paladin and Ranger.
3. Inspiration is an interesting idea that is very wonky in its execution. I've gone through several different iterations of it to try to make it work better and have a more significant and consistent place at the table.
4. The ability scores are still not balanced well, and don't offer enough to PCs outside of what they do for your class. All ability scores should have significant class-agnostic secondary benefits the way Con does. There's too much of a "stock build" issue for each class as it is, leading to too little diversity between characters and making character building feel shallower than it needs to.
1. Easily fixable, if you like to rough up low levels start at 2 or 3 with maxed HP roll /average after that.
2. I hate prestige class and MC except for CRPG, I am so glad you can build quasi "MC" in 5e with eldritch knight , arcane Trickster , or class X wit the criminal background. That is one if its finest game design features.
3. I love inspiration and it is in no way wonky. It is players last resort deus ex machina chance at my table and we normally allow it to affect a DM d20 roll also. It is a good reward instead of X independent of whether you calculate detailed XP or threshold XP
4. Yea there is some things about attributes which bother me a bit - but you would not be able to have bound accuracy were the attributes differently. I am to lazy to explain the math on it in detail now, but it has to do with the small prof bonus rang (1-6).
To make some attributes more meaningful use the "associate alternative attributes to skill checks" rule
e.g. perception with int, intimidation with str ( I also allowed it to be done with con wit ha dwarf once) etc. etc.