This is my favorite show of all time. I got my wife hooked on it when we started dating and she loves it too.
The show does change quite a bit over the course of the series. The first couple of seasons are smaller in scope then what happens later on. Initially, they are investigating individual incidents and helping people as they go, in that genre of show where a person travels from place to place, helping people and moving on. Kind of like Kung Fu, or The Lone Ranger. Later, the show gets much bigger in scope, until later on they are essentially the most important people in the world. I’m not exaggerating about this, but I won’t go into details because it would involve massive spoilers.
The show’s overall arc is very similar to The X-Files. Originally, it was very much a “creature of the week” format. Then they got into more of a larger arc. That show got bigger in scope as well over time (though not nearly as dramatically as Supernatural; then again few shows do change as dramatically). But both shows do get broader and focus more on longer, season-long plotlines, and the occasional “goofy” episode every now and then to change up the pace.
Incidentally, my favorite episodes of Supernatural were sillier ones. My favorite episode of all time is “The French Mistake”. If you are familiar with the film Blazing Saddles, the title of that episode is a reference to a scene in that movie where the characters literally break out of the film into the “real world” on screen, and that happens in a similar way in that episode. Other episodes along that line were “Changing Channels” and “Mystery Spot”. (The song “Heat of the Moment” by Asia was changed forever for me because of that latter episode, and I think just about every other Supernatural fan knows what I mean.)
I would say, though, that if the first couple of seasons of The X-Files aren’t enjoyable to you, the rest of the series probably won’t be, despite the major changes it underwent. And the same for Supernatural. I doubt that whatever you don’t like is going to be “fixed” later on, because it is still the same show.
I got to meet Misha Collins in-person at a convention, and got my photo taken with him. He is just as hilarious and charming in-person as he is on TV. He was my favorite celebrity to meet, and I’ve met folks like Norman Reedus, Nathan Fillion, and Tom Welling also. (There was a delay in getting photos done, and so Misha started joking with us to pass the time.)