As someone that stuck around since early season 2, I personally like both old runes and runes reforged. Old runes gave you stat buffs, and flexibility. I loved old runes mostly because I liked adding a couple of mana regen seals rather than scaling hp seals on mages to help with laning phase or Gold Quints on supports if laning seemed unbearable. I ended up having 15 rune pages (3 runes per role) by the time the new runes got released. (Grinded ip for all the rune pages i owned). As for the Masteries, the only notable similarites was that it was about the same utilities as the current keystones with addition to minor stat buffs. The whole idea of the old runes and masteries, during that time, was the fact that there was so much content, that many players wanted to experiment; to see which set of runes and masteries fit or would be fun with which specific champ.
On the other hand, Runes reforged adds more gameplay mechanics and while keeping the same feeling of flexibility but in a new and different form. One of the runes that I liked using was phase rush on tahm kench. In addition to building MS items, i could either get my carries out of bad situations really fast or draging enemies into my group for a quick pick. Another example would be using Glacial Augment on Braum. Most Braum player would take guardian for extra durability and shield for your carries. However with Glacial Augment, Braum now has a 3rd CC that applies on the 1st AA on a champ, making it easier to getting the passive stun to proc. Instead of having mixed stat buffs on runes and masteries, they replaced it with the new "adaptive damage" mechanic mostly to reduce the amount of champs that benefit mixed damage and getting more of one damage stat early on. Only exeption I have with the new runes is Conquer because of the consisent true damage on melee champs is unfair.
Only real downside for both runes was the amount of champions that abuse both old and new runes. About 1/3rd of the champion pool, between 2012-2016, were either mechanically dull or had debatable reworks. In addition to released champions and items (since 2011 to current) mostly having almost game breaking mechanics, whether it was just having too much consisent or burst damage, scaling into late game, or being unkillable. You can debate whether old and new runes were better but if I had one thing to say about Riot, League of Legends has a good track of breaking their game under multiple occasions.
