Garth Ennis hates superheroes, but he manages to both nail Superman's strengths and weaknesses in Hitman #34. Hitman is worth reading in its entirety, but this standalone issue won an Eisner with good cause.
SKO - my suggestion if you like DC characters is to branch out. There are some excellent Batman and Superman stories suggested here, but a lot of the best stuff in DC was produced when a creator was given one of the more obscure or lesser titles and given free reign on it.
Stuff I'd recommend:
Hitman - an excellent title authored by Garth Ennis, I believe the full series was re-released a few years ago in several volumes.
Suicide Squad - terrific series about supervillains who take on covert missions for the US Government in exchange for reduced prison sentences. John Ostrander's run in the late 80's/early 90's was outstanding but later iterations remain solid.
Grant Morrison's stints on Doom Patrol and Animal Man defy description, but should definitely be read.
I'm also partial to Justice League International, which came about when JM DeMatteis and Keith Giffen were given the Justice League to write but for various reasons were not allowed to utilize Superman, Wonder Woman, Flash or Aquaman. I think the resulting series was a lot more fun than the standard "WE ARE GODS LOOKING DOWN ON EARTH" stuff that the JLA books tend to traffic in.
CT gives good advice.
One rather recent series that I would also recommend is Secret Six. It's got a bit of that Claremont soap-opera feel, in a good way. It's a team of mostly also-ran villains who basically end up working together out of necessity, with all the bickering, alliances, and betrayals you might expect.
Forgot about the Secret Six, also highly recommended. Believe this crosses over with Suicide Squad at some point as well, since Deadshot is a prominent member of both teams.
For those who don't know, Deadshot is awesome.
