I have never posted here, but I saw this and felt the need to chip in. First, I applaud you for posting your video; it shows courage and passion for the game and the desire to want to improve. Secondly, your game is fine! If you are enjoying yourself and getting exercise and feel like you are improving, that is the important part. Thirdly, your game is a living breathing thing, it will continue to evolve, and so while there are many good observations about your video, they may or may not be accurate in another month’s time, because your game is continually changing.
If you want to improve your game there are many ways to do so. The first, as already mentioned above, is to find a pro if you have the resources to do so. BE SELFISH!!!!! Just because one person likes their pro, doesn’t mean you will. Don’t be afraid to try multiple pros out, this is a personal relationship and everything from how the pro plays, to their communication style makes a difference in how you learn. Pros are expensive though, and not everyone can afford one. If you do have the resources to work with a pro, get the most out of your lessons. A few tips (and I am sure there are many more good ones out there), don’t be afraid to take notes on a little pad. Either during the lesson, or if not convenient, right after the lesson. Warm up beforehand, so you are warm when the lesson starts, that way you use your full time for the lesson. I personally love video. It has been a while since I have taken a lesson, so this may no longer be the case, but a lot of pros I asked for video wouldn’t do it. I wasn’t sure why, but I could guess that maybe they weren’t comfortable analyzing video. Either way, things happen so quickly video is a great tool for a pro to break down your strokes.
Secondly, we are blessed with technology now that we didn’t have 10 years ago to help improve our games. You have already embraced this by videotaping yourself, an excellent idea. Leverage resources online. There is plenty of free content (the USTA [usta.com] has some good videos of various pros and their strokes.) Of course there is tons of stuff on youtube as well. There are various paid sites to also consider, such as John Yandell’s Tennisplayer.net, which has very good instruction articles and video (you also will see him posting here as well.) I personally think he is an excellent online tennis instructor (would love to take a lesson from the guy) and has a number of visionary lessons on his site. There is also Tennisone.com, where John used to be years ago and they also have very good instruction/ content, and there are countless other sites (fuzzy yellow balls, etc.), both paid and unpaid. You have awareness of where you are now because of your video, and you can compare this to where you want to be with online video of pros. Current state awareness, and future state target are important to making changes.
There are the more traditional methods as well such as reading books. There are plenty of excellent books on stroke mechanics/ technique, strategy, mental preparation, emotional stability, etc. etc. I personally recommend “The Inner Game of Tennis” by Timothy Gallwey (I hope it is still in print.) It is excellent! It won’t necessarily give you the stroke mechanics, but it teaches you how to learn (I know I am supposed to drop my racquet behind my back on the serve but never do, why can’t I do this and how do I change?) So it doesn’t teach you what you need to know, as much as it teaches you how to apply what you already know into your game. This book is read by coaches in other sports because the lessons it teaches are applicable to other aspects in life, a very good read.
Lastly, a word of caution. While this community is a great way to improve your game, tread carefully. People have different ways of describing the same thing (I say drop the racquet, someone else says swing it in a loop), there isn't always a consensus on how to do something, and people have different ways of interpreting the same thing. While I might give a piece of stroke mechanic advice one way, another poster might say the same thing a different way. You may take it to mean yet something different. Be careful how you take advice on these forums. There is a lot of great knowledge here, but make sure you understand what is being said. Heck, I have been to teaching pros that will either outrightly contradict each other on the same topic, or, will give the same instruction, but say it different ways.
So, keep playing and don’t get discouraged, your game will continue to improve! As you displayed a huge amount of courage by posting that video, it also takes similar courage to go to a pro. It is hard, especially as an adult, to have someone critique us. However, as you just exposed yourself to a whole forum in the name of getting better, I think you are already half way there.
I will repeat one thing that was already mentioned above. I am no tennis teaching pro, but do consider watching some serve videos online and try to incorporate some changes as soon as you can. Your racquet does travel a path on the serve that might cause some injury (I am no orthopaedic either, so take this as you may.)
Keep playing, it looks like you have passion for tennis, and that is the most important aspect of getting better! It will all be worth it when you finally break that bad habit, or you beat your big rival.