I definitely know my beers can be improved upon, no doubt about that. I am quite critical of my beers while I drink them, usually taking the time to taste it like you would a fine wine. I try to take down notes from first pours, around half a keg left and then when it gets towards the bottom, always looking for ways to improve or tweak the recipe.
That being said though, there has only been one beer I brewed that I didn't like and that was from a misjudgement of fermentation temp. Everything else I would put in at least the "enjoyable" category. Is it the best beer I've ever tasted? No, for sure it's not, but when I compare my beers to what else is out there for purchase, I feel I'm doing a pretty good job of making beer. I'm not trying to say that I am at a commercial level of quality and taste by any means, only that, for brewing at home, with a pretty make shift system, I brew a pretty enjoyable beer. I always look forward to filling a glass up and having a drink.
Now, I'm generally a glass half full kind of guy and well, I really like beer. I understand being critical of your brew, but to honestly not really like it? I just don't see the purpose of brewing. Yeah, I really enjoy the process, I like the fact that I am making a beverage, but if I didn't care for the final product, I'd really have to reconsider spending the time I do brewing.