The answers to your questions are dependant on what you want out of photography. Are you happy taking candids and quick snaps? If so, work on understanding the technical aspects of photography (proper exposure, focus, etc.) and don't worry about the rest. If you're looking to be more serious about it, and make pics that people take a second look at, then you have to concern yourself with things like composition, posing, lighting, etc. Ignore the praise heaped upon you by family and friends, they have an emotional attachment to the subject matter, as do you, so objectivity goes right out the window.
Crooked horizons. Well, you say it's a preference, I say it makes me tilt my head when I look at it. Since I don't walk around with my head tilted, I find it visually uncomfortable to look at pics with crooked horizons. I keep waiting for the bridge to slide out the left side of my monitor. I won't be the last person to tell you this. Convention is important. Convention exists because it's what most people like and look for, as well as usually being what's most aestheticaly pleasing. But again, if the pics are for you're own personal consumption, do whatever you want. OTOH, if you make them public, people are going to point out what they don't like, and what they won't like is your breaking from convention. Obviously, abstract and "art" photos play by different rules.
As far as the pic you posted further down, what were you trying to capture? Is the bridge the subject? If so, the building behind the bridge is a distraction. Was the building the intended subject? If so the bridge is a distraction. In either case, the branch covering half the frame is distracting. If it were possible, a different angle would have been preferable. The clouds also appear to be overexposed, and could possibly be recovered in ACR, but I'm not sure you can shoot RAW with your cam.
Keep shooting, keep posting, and above all, be thick skinned and open to the C&C you recieve. Nothing will create negetivity towards you faster than you defending everything you've done wrong by saying "that's my preference" or "that's how I like it" or any other constant defense of what people are telling you needs to be changed. If you make constant excuses, people here will see it as resistance to their experience and wisdom, and it never ends well. Welcome to the forum, there's a lot of resources for someone who wants to learn and improve.