What makes Eroica memoriable for me is that it doesn't force feed you the guy on guy. In fact it is 36 volumes of tension. You know that delicious sexual tension where you're wondering when exactly they are going to kiss (never mind do it already, as I'm pretty sure that Klaus's iron ass is still girded with the iron chastity belt.). It has very attractive men and but most importantly this series gives you 'dynamics'. Loads of it, and in a world of 'wham bam thank you sir..' that is in other manga, it's very refreshing.
Also this manga has 'story'. In a world where characters can spend pages staring into each other's eyes, in this manga there's always something going on, some coup to unravel, some fukkin' commies (yeah, un-politically correct now, but in the 70s that was what everyone called them) and the hilarity (the first volume when Dorian steals Klaus's tank, *not really a spoiler if it's in the first volume* you know that you've hit upon treasure.) Every single volume has had me weeping for the next volume and the last volume brought a tear to my eye since CMX is no longer around to distribute the series, that means that if no one picks up the liscense, then there'll simply be no more.
Eroica is not instant gratification, Klaus never comes out of the closet, and Dorian never quite gets to hit that but I think that there are tons of ficcers who actually write stuff that is fairly good, in character and who actually think about what it is they are writing. Due to the nature of Eroica in general, ficcing it is really a hard job since there's so much history you need to know, so much terminology and the characters are built in such a way that it's almost impossible for them to go in and screw each other automatically, which makes for fics that are wonderously vibrant and intricate.
I think for me the biggest payoff is/was the characters. The characters are unforgettable, when you get volumes in and you see Dorian and Klaus in action, then you realize that with characterizations and chemistry like that, sex would just be anti-climactic (though hey, imagination is a wonderful thing) and not to mention that you just learn so much about the characters slowly and surely, in little splurts.
I enjoyed my eroica ride and I sincerely hope that I can compel some of you to check out the series if indeed it sounds like something that might interest you.
On a completely unrelated note. Genshiken. I ♥ this series.