If I could take the 4e books (or a modified edited version) back to 16 year old me, I think I would be fighting tooth and nail to never play anything eles...
I say modified because I think the OPTION of a simple fighter (slayer/knight) is good, and I think that the latter editions of utilitie/skill powers and themes made major improvements.
I would also just take a black marker to any of the expertise feats, and pen in a suggestion to half the HP of all the monsters that are not solo/end boss monsters.
Look, I adored 4e. But not at first. When the game came out, I looked at it, even played it, and was like, yeah nah, I'll stick with 3.5 thanks.
When I got back into it a few years later, however, it was suddenly a way more exciting game. So many new classes and races, and they seemed to have realized some of the early powers were bunk (when I read that Wisdom was supposed to be a secondary stat for Wizards, I was surprised, since almost no powers require it outside of
thunderwave, which wasn't even that good...).
But when it became clear that the powers that be no longer wanted the game they had created, I was pretty annoyed. Even though I had just ended my 2 year 4e campaign because I tried to run White Plume Mountain and it fell flat because exploration wasn't all that much fun in 4e (and, well, let's be honest, a fight with a werewolf sorceress and her fighter boyfriend isn't a real challenge by 4e standards. Even Sir Bluto and The Crab were a bust!).
Because while I'd just run straight into the flaws of 4e in the worst way, I knew it was something that could be fixed if the devs would just work on it!
I recall having a real problem with my Death Priest. I'd invested heavily in Rituals so I'd have answers to any non-combat problem that came along. Right up until we were playing an LFR mod in Calimshan where we needed to cross a desert and I was like "oh, I'll cast this! and then that! oh and
phantom steeds!", and the DM looked at me and asked if I could save my residuum because otherwise there wouldn't be any adventure.
Even the adventure designers had given up on pretending the game supported the exploration tier!
So yeah, it sucks that it died the way it did, and that it took awhile for everyone to give it a chance (and it really sucks that so many people
still want to rag on it by saying "it wasn't D&D" or "it was a video game"), but let's not pretend it didn't have huge problems.
Whether or not 5e solved those problems is left up to the individual to decide...