I just got into SHINee(and K-Pop) the end of July this year, so I never got to go through all of the eras before Taemin grew up to be who he is these past singles... It makes me mad and sad. (At least I am trying to warm up to Nu'Est, though. They just debuted(ish).)
I am also a fan of Shinee since about August but think you should not feel sad or angry for not having been in previous eras, we should only support them with what we have available to us and I think that's enough.