Blue
Ravenous Bugblatter Beast of Traal
Now I've been a player for 6 months and I've noticed that I find character advancement really dull, something I never found in 3.5. Even playing as a wizard, I've found spell selection etc boring.
I'm the exact opposite - I enjoy 5e leveling much more than I did 3.5 leveling.
First, no dead levels. Finally getting enough XP to level and getting ... nothing but some math (HPs) was horrible. Most fo the classes had dead level - heck some spellcasters in 3.x had almost nothing BUT dead levels. If all you get is an increase in casting, and in 5e you get casting plus a feature - well, that's more exciting. The only dead level are if you take two martial classes to level 5, the second Extra Attack gives nothing.
The second point was that with prestige classes and feat requirements, we usually planned out a character levels in advance, if not a whole 1-20 build. "I need to have X ranks of this skill, which means I need to take at least one level of a class that has it as a class skill so I can go to lvl+3 max ranks instead of half of that, but I can't lose a point of BAB otherwise I have to wait another three levels for the feat I want next level...". The planning was needed to be able to hit the numbers needed to get the features we really wanted further down the road without delaying them too long.
Sure, the character creation mini-game was fun (and why I still occasionally build a superhero in Champions even though I haven't played in years), but leveling a character was just putting in place the choices already made for the most part, unless the character was diverging due to story or RP reasons.
Third, I have more freedom in building what I want (though less options at this point - which I approve of for other reasons). In 3.5 if I was going with a weapon wielder, I was pretty much limited to about 1/3 of the classes if I didn't want to lose BAB, which with iterative attacks was also the gateway to multiple attacks and being able to hold up your contribution at the higher levels. 5e your proficiency increases every level.
That's limiting, but spellcasters were much worse. Any multiclassing spellcasting among the core classes would level you too far behind since it wasn't additive. And DCs were by spell level, not character level. Prestige classes with +1 caster level were the only way to pick a different class and still be able to cast higher levels. In 5e, between all casting adding for spell slots and being able to upcast spells there's a lot more freedom in choosing what class I want to take for any new level.
To sum up: 5e does't lock features behind prerequisite gates so I can pick the next level I want to be, every level of every class brings something interesting, an more freedom in picking among the class choices because they stack better without overwhelming with a book a month.