Costumes that didn't looks like they take a decade to draw. Simpler is usually better. (I really wish Wonder Woman would go back to her George Perez costume.)

I wish I could say I miss the days before Event Series but I was 12 when SECRET WARS and CRISIS ON INFINITE EARTHS came out. So, I was born at the wrong time, so to speak. 

Marvel seemed to be finally getting its sh*t together in the late '90s, or at least trying to do so, and then Joe Quesada, Brian Jemas and Bendis proceeded to make most Marvel books unreadable for almost 20 years. 

I miss Wolverine still having a past clouded in mystery and Charles Xavier and Cyclops not being so morally compromised. 

DC's Vertigo and Wildstorm imprints. Not every title was a gem, but some really were. 

STEVE GERBER.  He was the best writer when pencilers were king.  He missed the era of writers being top dog, and I think he would have been treated very well then.

CURT SWAN.  Sort of the other side of that coin, he was sort of shunted aside just as writers (especially British and cynical writers) were on the rise.  I wish he could have kept working during the rise of the independents.  IRREDEEMABLE showed how a Swan mimic could do quite well in the modern era, and I would have liked to see Swan try his hand at crime stories like ROAD TO PERDITION and licensed classic characters (that are flooding the market these days) like DOC SAVAGE and THE PHANTOM.

MARVEL MAGAZINES.  I loved the format, color, and story approach of Marvel's magazines in the 70's & 80's.  The MOON KNIGHT feature in the back of THE HULK magazine is probably my all-time favorite comic.  And I enjoyed the b&w magazines too!  (Also loved THE SPIRIT MAGAZINE!)

MARVEL TEAM-UP and BRAVE AND THE BOLD.  Why can't we just have fun things like team-up comics again?

MARVEL PREMIERE and SHOWCASE.  Some of my all-time favorite comics are a lot of these one-shots (or two or three-parters) that gave great origin stories or new starts.

And I miss ONE VERSION of each character!  I'm so sick of, for example, the movie Superman being different than the Superman who appears on SUPERGIRL, versus the two previous movie Supermans, and the New 52 Superman versus the CRISIS Superman or Frank Miller's Superman or Straczynski's version, etc.  (When I was a kid, there were TWO versions of Superman--the Earth-1 version and the Earth-2 version--and they felt like separate characters to me...and I liked both of them!)

I agree with Eric about Curt Swan. Put him with the right inker -- like the late, brilliant Al Williamson -- and suddenly there's nothing "dated" about his style. 

When I look at the July solicitations for Marvel, it seems about a third of the titles are #1s. I'm not seeing any issue numbers above the low 40s. So when I see Captain America #12, I have to wonder, what exactly happened 12 issues ago? Was the series just renumbered as a marketing gimmick? Was the title rebooted? Was the entire Marvel universe rebooted? If I pick up an issue of Captain America from two years ago, am I reading the same character?

Why does Venom have a higher new issue number than Captain America? Why do the Runaways have a higher number than the Fantastic Four? Why is Squirrel Girl the most mature series in the entire line-up?

Once upon a time, I could go into a comic shop and find the latest issue of the X-Men on the rack. If I liked issue 123, I could go find issue 122 with high confidence that I would be reading about the same characters. At present, I have no confidence that I understand who any of these people are.

Spinner racks. (with sampler packs!)

One-shots.
Also (and not the industry's fault, obviously), summer vacations from school where I had nothing more pressing to concern myself with than going down to a convenience store or gas station to peruse the spinner rack. I'd plop down a buck for a comic book, a can of soda, and a candy bar.  I really miss that.  Didn't know how good I had it.