I generally agree with Sarg0n, chess is supposed to be an adventure. If you only ever play one opening, you are going to Disney and riding only one roller coaster the whole time.
Regarding e4 or d4, I used to hate d4s. The evident wish to slow things down annoyed me and struck me, as someone said above, as cowardly.
But with time, many many defeats and unexpected surprises later, I have concluded that d4 is just... A lot more interesting. it's sneakier. You both open yourself up to and allow yourself 20 different ways to be attacked or to attack. It can be much more convoluted, there can be a million centers plus a million hidden agendas. It's more rewarding for me.
These days, when I go for e4, I get bored. If I win, it wasn't that complicated, and if I lose it was for some stupid mistake. With d4, I crush egos or get mine crushed. If I feel smart and wanting to exercice my intelligence, I wreck the d4 games. If I feel dumb and blood thirsty, I kill at e4.
But this is very generalized. I'm sure in a couple of years I will be raving about how actually e4 is much more rich and complex in some subtle way.
In general, I try to dedicate myself to what I don't understand until I understand it. It seems to me e4 is not hard to understand, though it is hard to master, while why anyone would play d4 always baffled me, so I had to investigate : )