Be original and creative with each room. Make every room stand out.
Not every room can be a brand new idea. Sure you can use new and creative ideas throughout the game, but to expect every room to be unique and original and captivating is simply asking too much.
Think about Metroid, which many will agree is a very much loved classic. A lot of the space in that game is taken up by long hallways and corridors in which very little happens. There might be enemies scattered throughout, but a lot of it is just tedious travel. A long corridor in one area may be just like a long corridor in another area (gameplay-wise) with only a change in tileset and enemy sprites. There really isn't anything too creative or original about them that make them stand out. There isn't really anything difficult or challenging about them. They're just a way to get from one place to another.
Similarly, some rooms in Fangame are just there to connect the other rooms together. There are some rooms that really make you think or present engaging challenges, and in between them are other rooms that don't really have anything to solve and are just a way to get from the last room to the next. These rooms could be equated somewhat to those long and sometimes boring corridors and hallways in Metroid that just go to and from the more interesting places. However, being Fangame is an IWBTG-inspired game that caters to players with a thirst for brutality, rather than make rooms that you just walk through easily, I fill them with ridiculous jump'n'dodge obstacles. Part of the drive to get through them is to see the next interesting area.
Yes, some of the rooms use stuff like invisible blocks, and there are parts that are indeed "gimmicky". That's not a problem. It only becomes a problem when the game fully relies on the gimmicks to become entertaining. I'm sure just about everything in Fangame could be somehow tied to some sort of gimmick, but I think anybody who has played it can tell that I have definitely taken the initiative to try to do something different overall. Starting without the gun, for example, is something not often seen in the IWBTG fangame community. Most of the graphics are a little more polished and have more depth. The main character is 100% original. Etcetera, etcetera...
Also if you ever make an adventure game again. Don't use portals. It shows signs of laziness. Making areas flow into other areas looks alot nicer than just one second your in one place the next your in another.
Most people just accept the way games are made and just use their imagination. With you, I feel like I have to explain everything.
The teleporters in Fangame were the result of poor planning. No, the result of a complete lack of planning. I originally had a door that led to a darkened cave area. I'm honestly not sure how it turned into teleporters. Perhaps if you watch my "History of fangame" or whatever I called it on YouTube, it'll explain why I started to use teleporters. Maybe I didn't mention it. I don't remember. I should watch it again. Anyway, it was the best I could do at the time I implemented it. It made the most sense then.
FYI: There are already a lot of things about Fangame that I would not do in future games.