The big stuff: a spouse of mine would have to agree with me on childrearing philosophy for the most part; we would have to have similar priorities and values (e.g., family is most important; making a comfortable secure living is important; career for its own sake is less important); we’d have to be on the same page with money; we’d have to have similar ideas about partnership (I want an equal partner, though I’m totally fine with preferring different jobs – I do a lot more childrearing duties, but mr. hunter does more housework).
The more specific stuff that was important to me: To make the relationship work, requirements of mine were for someone with the same sense of humor, who was good at technical work (that’s a random bias and dealbreaker of mine), who was laid-back, who was supportive of me, who was patient with me, who was non-critical, who was able to discuss things reasonably instead of fighting even when he was upset, who didn’t fight dirty. (Not to denigrate people who aren’t patient or who do fight – I’m not horribly patient myself – but specifically because of the family I grew up in, it was very important to my mental health to marry someone who had these specific character traits.) A spouse of mine would also have to be able to discuss things rationally, and consider my point of view and argument even if it didn’t agree with his. (He wouldn’t have to agree, but he’d have to at least attempt to see my point of view.) Oh, and have good grammar. I couldn’t deal with someone who couldn’t spell or who didn’t know the difference between “its” and “it’s.” Oh, and someone who didn’t want to be joined at the hip all the time (broke up with one boyfriend over this – he found a girl who was very clingy and I think they are very happy together).
The things that turned out not to matter as much: I’d always thought I wanted someone really musical, you know, the sort who plays several instruments and sings like an angel. mr. hunter can carry a tune, but that’s about it. We have different political beliefs, but that’s ok because we rarely talk about politics. We are of different religions (I would rather have married inside my religion, I suppose, all things being equal), but that doesn’t matter because we have the same general attitude towards religion (it’s important to us, but we are cool with mocking it too). I also thought I liked dark slim guys, but mr. hunter turns out to be a blond blue-eyed tall guy, so that went out the window too! He doesn’t have a whole lot of ambition and even less wish to be social, which I suppose I’d slightly prefer. I’d probably also prefer someone who wasn’t quite as much into doing his own thing and maybe slightly more into couple things, although we’ve pretty much settled into a groove with that.
My husband’s list was something like my first paragraph, I think (he’s a little less picky than I am), although he got several “freebies” – we share pretty much exactly the same sense of humor; I am mostly-rational (“more-or-less,” he’d probably say); and I’ve got a technical background, which he gets a huge kick out of. And we like the same kinds of books (which was a freebie for me too; I would have been happy marrying someone who didn’t). He’d probably also add that he needed someone who wouldn’t nag him – he is utterly allergic to that – and someone who was comfortable doing her own thing.
A.Selene, what kinds of things are you picky about? That would help answer the question of “are you too picky?” Big things (matching values, priorities) I don’t think you can really be too picky about. And it’s okay to have a couple of dealbreakers, like spelling 
But too many of those, and yes, you’re getting into too-picky territory.