How do I know what good espresso is

Hi all,

Just wanted to pop on here and ask if anyone else has had this exprience. I've been trying to make a nice tasting espresso for a while now, but I haven't had the best experience. I've pulled about 3-4 dozen shots now, and every single one of them has tasted off in some way: Very sour, very bitter, sometimes both.

I've been using 12g in, getting about 30g out in 25 seconds, using a light-medium roast, which from what I've seen online should taste nice, but it just doesn't. I've gone 2 clicks finer and coarser from this point and all shots just tasted sour/bitter. I feel like I can't really distinguish between the sourness and bitterness either, it feels like they're always both present.

I'm starting to question if I am doing something wrong, or if I actually just don't like espresso. It tastes nice when I drink it with milk, which is the way I've always drunk other coffee's.

I hear people talking about sweetness in espresso a lot, and I just haven't been able to get any of that. Am I just still doing something wrong?