>>96973611(sorry for the blogpost)
I've given this matter a lot of thought over the years. Where I grew up in Europe, 90% of the comics published were Marvel (Spidey, X-Men, Avengers etc.) during my childhood. Only hopped on the DC train in 2008, with Johns' GL and Morrison's Batman, and I haven't looked back ever since.
Yes, they ARE fundamentally different. The main difference IMO is that DC's heroes are much more 'mythical', godlike, larger than life figures, rather than complex human beings (hell, this thing was even emphasized in runs like Morrison's JLA). This is mostly due to the fact that many of them were created before Stan Lee brought a new type of characterisation to comics in the '60s. This manifests in some ways like:
1) generally, DC's heroes are much more powerful
2) the 'legacy' aspect: we've seen literally hundreds, if not thousands of different versions of Superman, Batman, GL, Flash etc (in Elseworlds, possible futures, different universes, or characters inheriting a mantle). This is an important part of passing down 'myths', and again, this has been emphasized in lots of DC stories.
3) as a result, DC characters lend themselves better to out of the world settings, and with grand concepts, like the multiverse, the speed force, fifth dimension etc. This is very subjective, of course, but I'm looking for escapism in comics, big, (not necessarily) dumb fun, that's a major part of why I love them better. (That's not to say I don't enjoy Marvel's more grounded efforts, like Ennis' Punisher, I'm just not as fond of them.)
4) DC's publishing history: if you read their history, look at how long certain comics been published, how the Flash of Two Worlds story came to be, how they brought publishers like Charlton, the core concept of the multiverse and 'myths' have always been in DC's DNA! This logically leads to the fundamental differences explained above.