I don't have any stepkids but I will say that I think it all depends on how much effort you put into it. I was a step kid when my mom remarried after my Dad died. My stepfather very clearly preferred his own children even though they used him for all they could and didn't treat him very well, and my mother made us treat him with respect, just like a real parent. My mother went above and beyond to treat the stepkids the same as us, to the damage of my brothers and myself. Things like my stepsister who decided she wanted to be at her mother's most of the time because there were no rules there- her mom would buy her alcohol and allow her boyfriend to sleep over (at 15, we're not talking college here), etc.... so of course she wanted to be there instead of our house that had rules

But even though she only came for 4-6 days per month, she'd get the same back to school clothes budget, the same number of pairs of new shoes, etc..... it was really disproportionate.
On the flip side, if you are a stepchild, do you love your stepparent as much as you love your biological parents?
not a freaking chance. Between all the b.s. he put us through with his kids and he wasn't as nice to my mother as he should have been, but in the end he totally used my mother and then left. No way do I care for that guy at all, let alone nearly as much as I did for my father.
Now my mom has, oh gosh, I don't know what to call him, a companion maybe..... they're not really dating but they seem to be best friends, live together as roommates, do most stuff together, etc.... now he is the nicest person. I know I could call him if I needed anything, he would help. He loves my kids, he's great with them, he's just a genuinely NICE person. But I don't have fatherly feelings towards him, he's more like a cool uncle.