I certainly wouldn't say I have "horrible" in-laws, but that doesn't mean I don't have my ups-and-downs with my MIL (she's a widow, so no FIL), just as I have my ups-and-downs with most members of my family now and again.
To reply to the OP's questions:
a)are you absolutely sure that its not partly your fault?
I think "fault" is a bit harsh, but I do agree that most disputes arise because of false expectations on both sides. My MIL had very set ideas about what she wanted her DIL to be like (I'm not over-analysing, she told me once) - a jolly, "to the point" girl from the country that you can share crude jokes (she was using the example of a neighbour's DIL) and talk about gardening with, probably someone just like herself. I can appreciate that as a MIL, it may be slightly hurtful to think that your son chose someone who doesn't reflect your own personality (I don't have DCs yet, but I imagine that would be the case). Sadly I'm a city girl, quite reserved and sensitive, and I think she finds my personality rather "foreign". Equally, I have a great relationship with my own mum, and probably "expected" to be able to "win my MIL over" using the same things I knew my own mum would enjoy (taking her on spa days, on city breaks, going shopping). When MIL showed her displeasure/lack of interest/outright criticism of these things, I felt a bit hurt.
MIL is also very assertive, and in that respect, it's my fault that I didn't dare to be equally assertive with her early on. So things would eat away at me and when I finally did criticise her, it was very out-of-the-blue and hard for her to deal with.
b)what would you want your in laws to be like on a daily basis?
- Stop keeping a tally on how much time we spend with the respective sets of parents. My parents live in another country (MIL is a 2-hour drive away) and I hate having to justify why I went to see them for a week but will only visit MIL for a long weekend, or feeling bad about going on holiday with my parents because MIL won't be getting the exact same "time slot".
- Be more proactive in visiting us/suggesting things we could do together, instead of moaning that we don't visit her enough and having to be "officially invited" at least 3 times before she does come to visit. Constantly moaning that someone could visit you more often is just going to want to make them visit you less, and sentences like "I really miss spending time with you, let's meet up next week" work better than "I've counted and this is the first time you've been up to see me in 6 weeks".
- Accept that your DIL will have different interests and opinions, but that they are not better or worse than your own, just different.
- Accept that your DS is not a sheep who does things just to please his wife, but actually might want to do these things himself, even if he didn't express an avid interest in them in early childhood.
- Most importantly for me, try to maintain some sort of relationship with, or at least interest in, your DIL's family. The fact that MIL dislikes/doesn't feel comfortable with my family is a major source of tension, because we can never bring everyone together to celebrate things as a family. I'd like MIL to feel that my relatives are now part of her extended family.