Mr. Magniloquent didn't present it in the most magniloquent way.
Attributes serving as saves means: 1) 6 saves instead of 3, more appropriate saves vs a danger. Reflexes being based on Dex and Int was retarded. Now you can use Int to save vs some mind tricks, not just Wis and Cha. And you can't use Int to physically dodge stuff. It is more intuitive. Someone wants to shove you, Str save. Easy. Opposed rolls and saving throws use the same unified mechanic. 5E gives much more importance to attributes and makes them the core of the system, which is how it should be.
Attributes being capped means: Fuck the over the top min-maxing, characters can diversify a bit. But note that you can exceed the cap in some rare ways; 30 is the hard cap. But it makes anything above 20 superhumanoid.
Feats being more substantial is good. More power to customization of characters, no useless feats, all character-defining.
Weapons not having +1-5 bonuses means you won't have to choose between accuracy and damage vs magical effects. All magic items are magical in other ways than giving numerical bonuses. It's no longer a stack-the-bonuses game only to have a chance to be effective. Magic items are great again. Also, this + the attribute cap allows for a non-level-scaled world: low level adventurers have a chance against higher level enemies if they're clever and use all advantages, since they don't need to gain mass bonus modifiers to have a chance to affect them. This is great incline.
Advantage/Disadvantage is a great mechanic at the table. Easy to adjudicate, one rule for all situations, not +2 for this, +5 for that, +3 here, those two modifiers stack but not those two; just compare positive and negative circumstances to determine if there's an advantage, a disadvantage or not. Also, you roll more dice! Way faster at the table, and statistically similar except in the extreme stacking cases which were broken anyways.
Alignments are not gone despite what Mr. Magniloquent said, just less strict. They're strong tendencies. So a lawfully aligned character/monster will have a strong tendency to go with the law, more than usual. Dwarves for examples are listed are usually lawful, while Humans have no intrinsic tendencies. Creatures acting on the basis of instinct rather than morals are now unaligned, much like retarded people. But now in addition to Alignment, you've got Personality Traits, Ideals (ex: honor), Bonds (ex: debts) and Flaws (ex: greed) to further define your character, with some small mechanical backing for them (Inspiration that you can gain). There's no Detect Evil spell in the base rules though, which is a good thing because it fucked campaigns based on subterfuge and deception.
As for prestige classes, what has been done in D&D 5E is to give much more customization options within a class. Some class features are there for all members of a class, some are dependant on an archetype path that you choose (and there are choices within each archetype). It's a much more modular design. For example, Wizard school specialization is handled with an archetype that gives appropriately themed class features for the chosen school, not just +1 spell slot of your school and two forbidden schools like in 3E. So basically classes have more variability, which reduces the need for prestige classes to further define your character and give them a twist. It's all right there in the base classes. And it also allows for supplements to add archetypes, or for you to design your own if you're into homebrewing.
Anyways, I could go on, but 5E is far from trash.
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