These are the games that I made with monogame. The first one was a horse racing game, but all my codes and images were deleted because of some reason so I draw runners and made it a running race game again. All drawings belong to me (all animated) I m not a very good coder ; its only six months time I try to learn C, and then C++, and now because of monogame obsession, C#.
But I get bored after some time. Because I want to do something different. There are millions of space games, millions of race games and millions of trading games. I want to learn what your games are about. Can you find something different? Do you sit and write a story for your games? I dont want to work on something ordinary. Any new ideas?
This may sound harsh, but today you’ll hardly be able to find something that hasn’t been made. Ever so since game development has become more accessible to people (not just old-style programming, but also tools like Unity which bridge the gap and various game makers), people have virtually tried most of the ideas. Sure, original ideas are out there somewhere, but there’s a veeery big chance that an author, in search of an original idea, will use something someone else already used.
That doesn’t have to be a bad thing though, as it’s not the genre and setting that define the game by themselves, but also how the creator(s) execute their idea. Mass Effect is a space sci-fi opera, which is not something original (Star Wars existed for decades before, to name the most obvious example), but it differentiated itself by the way it presented story and gameplay elements, alongside other things.
That being said, right now I’m working on the variation of Civilization game (that is, 4X strategy game) set in fantasy setting, learning 3D along the way. I asked a friend (who’s writer) to adapt the fantasy world he’s using for his pen&paper roleplay, since I’m pretty bad at making all that stuff up by myself. On one hand it is an ordinary game as similar games do exist, on the other hand I’m trying (or at least will try) to put my own spin on it.
I don’t think there is any issue with making something that was already done. You will still add something from your creativity which will make it different and hopefully more enjoyable to some people, who knows.
I have same approach as @Aurioch wrote. Add “the spin” on a game (mechanics, story, setting, hand drawn graphics…).
In the end it depends on your players not on yourself to decide if the game is good.
Also look at all the second and third versions of the games, mostly they are so similar almost in every aspect but people still play them because they like to have at least some new content.
If you get bored during development I think it is normal. I don’t believe those guys saying they are all excited all the time. Currently I am making maze-solving game for mobiles with “the spin”.
There was initial stage when most gameplay code and features were created in large numbers with great excitement. Since then it is more of a normal project with a lot of boring aspects going along. All the time I am already thinking about new games I want to create with some sketches already done 
but waiting until this is finished.
I am very similar to you, tho in my case I’m a bad designer so I usually get bored because I have to do all the art for the game. Pretty much all of them I create just for my own enjoyment tho, so I can abandon them when I get bored of them. As for the idea of a game, usually I just know the base concept of something I want to make, and I start going from there and add new stuff as I go along, makes it more fun and exciting IMO.
The only game I did publish screenshots for was something of a text adventure game from a platformer perspective: loading animation, game. I also made sure that titles of each screen were hints for the screen itself, for example on 3rd screen, if you tried saying “move left” the stickman wouldn’t move, while saying “don’t move left” would make him move. Something similar has been done for [2rd screen] (https://twitter.com/cra0zy/status/713799647999967233) (screens are numbered by the order I added them in, I was also making sure first few screens are easy to solve).