Canon EF 28mm f/1.8 USM - landscape
You should be at f8 or above for these scenes, especially as the 28mm doesn't have great corner sharpness. Even better, mount it on a solid tripod and focus stack. i.e. Focus for infinity and get a sharp horizon. Take a second shot of the foreground and a third of the middle distance. Combine them in photoshop taking the best parts of each.
There is something else wrong with the pictures. Possibly over sharpening? They have a high ISO plastic-y look that ISO 100 shots shouldn't have. Definitely run through some online basic landscape photography tutorials. You should be able to get some large technical improvements in your pictures with just a bit of study.
I have the lens. It's not bitingly sharp even stopped down, although the center is fine. It has CA and is prone to flare without a hood.
I love it though. It's light, and silently focuses very fast. I use it on APS-C or APS-H in dark nightclubs, always with a hood (which should be included - Canon I'm looking at you you cheap @#$%). Even if I'm not using it wider than f2.8, it's extra light gathering really improves auto-focus speed in available dark photography.